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Preservation's power was also in the Mists and other places while Ruin was strictly in Atium.  Preservation built/modified the system specifically to siphon off and trap Ruin's power so it's not a really natural and/or balanced process.
 
 
 

It goes faster due to the elimination of friction, but it still faces inertial drag forces from the mass of air that is getting shoved out of the way as if goes by.  As it speeds up and approaches the Speed of Sound (for Roshar's atmosphere), the friction matters less and the inertial forces become more prominent.  

Unless there ends up being something extra special about the Honorblades that makes them burn differently (as a Feruchemcially charged metal, which they resemble) the easiest source of godmetals is broken Plate.  You can easily break pieces off (compared to the practically invulnerable blades), and then use it as a distillation machine to turn Stormlight into Godmetals.  
I think we will eventually learn if/how Honorblades can be repaired, and what that looks like might illuminate all this.  

No to Muscle memory: 
 
 
RE Compounding, we dont know and he's staunchly RAFO'd all questions.  Personally, I think it allows for Copying the Memory (either making copies in Metalminds or Allowing you to retain it while storing).  Otherwise it seem waaaay too suspicious that Hoid managed to get such a uniquely incriminating first-hand Memory from That Guy. 

Generally, even if it was your own investiture, it would scramble things enough that you would not be able to recover it.  When you burn a Metalmind to get the Feruchemcial effect it is magnifying whatever the existing Charge would do, so I think it would do the same Nothing that the Metalmind lets you tap.  Alternatively it might behave like a bad alloy and make the Allomancer sick. 
 
 
 

Since a Shard's power can gain sentience all on it's own, kinda sorta sure but maybe No depending on your definition of Vessel. 
As far as I can tell below, he's saying he see's a difference between a Person that has become the Vessel of a Shard's power and a Super-spren that is the Power itself gaining sentience.  But the people in-world that dont believe in The Beyond and/or see Spren and Souls and Cognitive Shadows as all the same basic thing might argue that there is no meaningful difference.  
 
   

Short answer is no.  Long answer is that there are several factors.  The base lashing is always relative to the Object or Person being lashed, so the starting point is that weight.  From there the efficiency of the lashings are scaled by the strength of the Bond that is providing access to the Surge.  The least efficient means is probably a Fabrial followed by the Honorblades since they barely Bond.  Most efficient is the 5th Ideal Radiant, and all the lesser radiants and squires fall somewhere in the middle.  I have no idea if Squire strength is static or scales with the radiant's Ideals, but I suspect the latter.  

You would struggle with it quite a bit, depending on how heavily Invested the metalmind is.  Assuming you could make it work (both a skill and a Power issue), it would likely work the same way as if you melt one down and try to alloy it: the investiture remains but becomes inaccessible until you changed it back.    But when asked directly he effectively RAFO'd it:
 
 
 

Broadly speaking, Lerasium is a way to make permanent revisions to a spiritweb, and Im assuming will become relevant in the sci-fi era 4 if not before.  Depending on how complex those changes be manipulated via scientific alloying, it might be possible to do quite a bit of targeted manipulation, with something comparable to forgery being the upper limit I can imagine (essentially just housed in chemistry instead of symbols, and also permanent). 
We know there are effects if alloyed with the 16 metals of the metallic arts, as well as any of the godmetals.  I suspect there would be an effect with Silver, which is the only known example of a metal that is cosmere relevant without being part of the metallic arts.  I also suspect you could change the effects by alloying it with charged metals (such as metalminds or awakened objects) the same way allomancy treats feruchemically charged metals as essentially a new viable metal.
As a limit, ultimately the effect happens when a person Burns the alloy, so I dont think it would easily interface with gems or other non-metals in a fabrial arrangement. 
I have no idea if or how it might interface with Ettmetal, in a Primer cube or as an alloy.  
 

Spren are pure Investiture.  Generally speaking Investiture can either Invest into a pre-existing object/person, or it can manifest directly as a form of matter itself.  When it does that it takes tons of Investiture (along the lines of manifesting a cheeseburger using electricity and and E=MC^2).  For mostly thematic reasons solid Investiture tends toward metals.  Liquids are the most "powerful" because they are dense but not settled into a specific form and function.  
Spren can manifest their Investiture as a full physical object only when they have enough Connection to something in the Physical realm to act as an anchor, which the Radiant Bond provides.  
Cognitive Shadows are also Pure Investiture and are functionally very similar to Spren, but they are distinct in a few ways.  The biggest Ive seen is that Cogntive Shadows were once mortal (with their own physical form) and unless they were restored nice and quick (like Szeth) they need some external Investiture to support them (weekly Breaths, Oathpacts and other massive infusion of Investiture by a Shard, etc).  I suspect that Spren dont require the same sustaining external Investiture because they arent being Pulled to the Beyond; but Beyond questions get no answer as a matter of policy.  
 
 
Burning a Rosharan Godmetal may or may not work out of the box (without a Connection to those Shards), but it would be viable, not inert.  The most recent answer is "it would do something".  We do know of that one Allomancer that has a tie to Rosharan magics now, so he might be able to do it.  I assume it would be harmful to the spren, though Plate might be able to heal with Stormlight.  I'll be curious to see if different Plate that comes from different species would have different effects (windspren vs glory or logic or creationspren, etc).
 
 
   
 

Spren-sized, yes.  Actual fraction of Infinity as with the 16, nope it wouldnt fit.  There are physical limits to how much investiture can be crammed into a given chunk of metal, and Shards are too big.
 
 
 
 
 

What follows is language about Language that I do not understand, but may be relevant (something about how the K in Kholin is pronounced):
 
 
EDIT: To take a stab at your actual question: When english spelling is not compatible, they seem to go phonetically as close as possible. This is similar to how you will see English translated into Japanese for example, where nearly all the consonants are paired with a vowel. We saw this in how they "wrote" the other planets like Scadrial and Nalthis with extra vowels (Scadarial and Nalathis, iirc). For all practical purposes, C is pointless in modern english; it has no sounds that is not covered by S, K, or CH. I would anticipate they just substitute for the closest appropriate consonant. 
I had a teacher in high school that argued C and Q should both be re-purposed to capture the SH and CH sounds.  He was more sparking critical thinking than trying to re-work the language, but he made some good arguments.

The power in Hemalurgy comes from the fact that it is ripping a chunk of functional Spiritweb from a person and splicing it into somebody else's, potentially including the piece of their soul that gets Allomanic Power from Preservation (or any other shard/magic, in theory).  It's doesn't replicate those other effects or powers, it Steals and splices the bit of Soul directy.   
Generally, the first one in line Donates the Spiritweb, and the second receives it.  This is more or less how the Inquisitors did things in The Final Empire to prevent decay. 
That being said, Intent is pretty key to a lot of Hemalurgy, so it's possible that you could load a single spike with multiple donors and then grant it to the last in line. But it is hard to Invest something that is already Invested, so there will be resistance the 2nd and subsequent times.
You cant empower multiple people with a single Spike because the spike needs to be left in the person to do actually anything, literally stapling the two people together.  However, You can charge a spike and then physically split it, keeping a proportional amount of power in each spike piece.  

The Bond would have been possible in theory because the underlying realmics should be the same.  As far as we know nobody back then figured such a thing out, but Connection is a cosmere-wide thing so we could be wring.  That being said, we've been told that a) Adonalsium would have actively prevented spren from granting surges, and b) any spren that did exist would have been reassigned to their closest Shard.
 
 
 
 

Sel is a corner case.  The Focus of all the different Investitures is Patterns/Symbols, as is evident in AonDor, Dahkor, Forger, etc.  However, they fundamentally work differently than all other know Investitures.  This is because all of them are sourced in The Dor, which resides in the Cognitive Realm instead of the Spiritual Realm.  What happened was Odium came and killed/Shattered both Shards, then for reasons that arent 100% clear shoved all their investiture into the Cognitive Realm rather than letting it return/remain in the Spiritual Realm which is where the bulk of most Shards exist.  Among other things this is why all Dor-based magics are fundamentally location-locked, so they all loose strength the further you get from their respective homelands, and all of them fail off-world (unless unrevealed special measures are taken).

It's a Horneater thing.  Some (but not all) of them have the ability to see spren even when the spren are not trying to be seen.  They call such people alaii'iku.  We assume this is a result of the fact that Horneaters as a race have Singer heritage.

Maybe, thought I tend to think of it more than they've evolved to just naturally sense more of the realmic interplay that makes up reality.  In the same way that their Gemhearts are confirmed to form via leakage from the Spiritual Realm, but I dont personally think of them as a magic system so much as simply how life works on Roshar where the realmic boundaries are so much thinner.  On the other hand, we know Roshar was Created specifically and unnaturally by Adonalsium, so maybe calling it a Pre -shattering magic system is more accurate
 

I dont think so, Spiritual change and/or damage alone doesnt change your Identity enough to make Metalminds inaccessible, even when they are specifically messing with Identity.
 
   
 
 
  Wax is a bad example when it comes to savantism, WOB has it that he's going to recast his abilities as skill-based rather than savantism, which was intended to always have significant downsides and has drifted from it's original intent.

When he swore the 3rd Ideal to follow Dalinar, he felt a sense of Approval from his spren but said it "rarely showed itself to him, even then." (OB Ch.121)

Nope, to the best of my understanding they shouldnt interfere, they are operating on different mechanism in that the medallions dont actually make any real/permanent alterations to the user's spiritweb, which by extension means the web is not being damaged enough to give a Shard the same backdoor access that spikes do. 
That being said, we're pretty sure that hemalurgy is involved in the creation of medallions, and at least one fairly detailed theory by @Calderis speculates that the reason medallions (other than the Bands which are weird) have a limit on the the number of powers they can combine is for similar reasons, but the mechanism involved is a more of a Connection Interference issue rather than the Spiritweb Crack/Decoherence problems you have with with actual spikes. 

Nightblood is weird, it completely Annihalates it's target in All Three Realms, and then if Im not mistaken absorbes all the converted Investiture.  By comparison shardblades damage the Soul, but there is enough left that it can still be healed by F-Gold, Regrowth surge etc, so presumably Odium can consciously restore them.  Nightblood prevents that because it Eats ALL the pieces.
As I understand it (though it is debated) all planets are going to have fairly unique Cognitive Realms, influenced largely by the population's collective expectation/image of it.  Thus Roshar has a Gem theme, while Metals glow and act as a window/gate to the Spiritual Realm on Scadrial.
Strongly debated, no resolution.  Based on Harmony, it seems unlikely to me that you'd be able to maintain any sort of balance with that many competing Intents, especially at ten.  There are arguments that certain combinations might work better together than others and make it possible.  On the other hand, once you have several already, adding another is going to cause less and less upset.  So if you could get to 10, Id think the next 6 would be easier that the last, but I wouldnt bet on anyone in particular being able to pull it off (other than that obvious dude). 

Fair point, in the case of Harmony specifically; represents everything that made the planet so should be able to unmake it.  Thought it would likely push whatever internal balance he has over the edge, unless maybe shoving it into the Cognitive Realm is "Preserving" Scadrial enough to be a balance to Ruin's side finally getting to wipe the place from actual existence (ie the Physical Realm).   I tend to thing that trying to get it back might be much more tricky.