Honorless

It would depend, if there was someone who was like a Vessel of Adonalsium, then they're just dead, so joining them together won't bring them back. If Adonalsium was the power itself, then would joining the Shards remake it, or would it create another new entity?
The Dawnshard mural does imply that they were used to Shatter Adonalsium, each of them pulling apart four Shards, but we have no solid confirmation from Brandon, nor any bigger hints in the books yet.

This post by @Pagerunner has a thorough breakdown about the Surges we didn't have a lot of info on, it's from before RoW so it doesn't have any spoilers / isn't updated with any new info on the Willshaper Surges:
 

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Hemalurgy just patches a piece of stolen Spiritweb over your own Spiritweb. Powers stolen by Hemalurgy are not inheritable.
Koloss produce Koloss-blooded children, they become Koloss upon accepting Hemalurgic spikes, as we see in Allomancer Jak.

Silverlight isn't on a planet, it's a city situated in the Cognitive Realm inhabited by Worldhoppers and descendants of Worldhoppers

Well technically the Voidbringers are the Ashynite humans
 
The Fused, though they look like Singers for the majority of OB, look more like spren when they're not possessing a Singer body, as we see in Venli's Interludes, see the chapter "This One's Mine", iirc. They inhabit the original Singer's Gemheart, which unlike with Regals, kills the possessed individual. There is no bonding going on between the two. The original is killed and their body's patterns shift into the Fused's.
Besides, Oaths are Honor's purview, not Odium's 

Ancient Radiants did not believe she could corrupt highspren (referring to either sapient spren or Nahel Bond capable spren) at all, yet she clearly can.
She shouldn't be capable of Corrupting Bonded spren, as that would've been a huge advantage for Odium to do nothing with.
I would say there should be ways to change Corrupted spren back but they wouldn't just naturally turn back to their previous form, she's probably affecting their Identity somehow

We don't know much about Hoid.
He's from Yolen.
He knew the Vessels of the Shards of Adonalsium and was involved in the plot to kill Adonalsium alongside them.
He has a form of immortality, as well as time dilation, and various pre-Shattering magic including a form of Lightweaving. He has access to Fortune, he can tell if he's going to be needed somewhere sometime. He goes around traveling the various Shardworlds, collecting magics.
Hoid isn't his real name. He has many names like Cephandrius, Topaz, Lunu'anaki, Midius, etc
You might want to check out his Coppermind page here:
https://coppermind.net/wiki/Hoid

Ah, there's an underlying question of whether the Mists are truly a gaseous manifestation of Preservation's Investiture or not. Steam is water in its gaseous state, while mist is composed of small droplets of water in the condensed phase. The Mists might be like the latter. The same can be asked of Stormlight which literally arrives with a massive rainstorm. But gaseous is how Sanderson describes them.
Either way, it shouldn't matter. The Mists aren't composed of water but Investiture so they should be able to turn the Sand white just like Stormlight, which we see an example of in-book. Unless there's very high humidity (which isn't necessary for the Mists to form), Mastery should be possible.
In case the above WoB is confusing, it means that just White Sand and Investiture does not a Sand Master make. You need to have the necessary component in your Spiritweb. But if you are already a Sand Master then you can recharge your Sand with any kinetic Investiture.