The Sovereign

Silver isn't Investiture inert. Duralumin and Aluminum are. As Tanavast says it is like Aluminum but not the logical leap is that it is an Aluminum Alloy with similar properties; I.E. Duralumin. I hadn't really considered the amplification property of Allomantic Duralumin, but I don't believe that is what happened there. It seems more likely to me that was the result of Honor and Odium's clash breaking the shell of (maybe)-Duralumin that was shielding the Perpendicularity and the surge of power was a resonance with Odium's Perpendicularity.

Just picking a little bit of a nit here; I don't have my copy of WaT in front of me to get the exact quote, but Tanavast makes a comment along the lines of "it was like Aluminum but not". The 4th moon was probably Duralumin, not Aluminum.

We don't know the specifics, but presumably a human loyal to Taravangian in the tower stole it while Dalinar was in the Spiritual Realm. On WaT page 1210 he said said:

This is definitely speculation, and correlation doesn't imply causality, but go back in reread the description of The Nightwatcher (specifically how she moves around) in Oathbringer from Dalinar's trip to "The Valley" and compare it to the description of Ba-Ado-Mishram in the Spiritual Realm vision where she is healing the wounded Singers. The way they pull themselves across the ground is very similar. We know from the Sibling talking to Navani that the Nightwatcher was created when Kor Cultivated part of the Great Ado Spren "The Night". I suspect BAM may have been the result of Odium Unmaking whatever remained of "The Night".

I hadn't even considered that the partial connection to a Hybrid light being the cause for the light to drain out so quickly. This seems obviously correct to me now. As we have seen with higher Ideal Radiants, the stronger the Connection, the less porous the Radiant.

I think we should look to Lift here; Her Surges are fueled by Lifelight and she can use Towerlight. She cannot use Stormlight. To me this would indicate to me that if you have the Connection to access one of the Lights that makes up a Combination Light, then you can use the combination Light. With that said, Lift is weird and the normal rules don't apply to her could absolutely be in play here. Regarding Venli, we know she can fuel her Surges with Stormlight, Voidlight, and Warlight. Regarding Kaladin when do you mean? At the end of RoW while fighting Lesian? His Eyes glow Gold/Red due to a connection to Odium, but he is definitely using Stormlight there. Or do you mean at the end of WaT? In that case he swears the 5th Ideal and the uses the burst of Stormlight from the swearing to fuel Nightblood for Szeth.

Using Towerlight as an precedence, it seems likely that anyone who could use Stormlight or Voidlight will be able to power their Surges with Warlight. Once the Fabrials are configured to Warlight, then Fabrial technology should progress normally (provided they can get access to Warlight, which should be pretty easy provided that the Listeners have easy access to it and already have trade contracts in place with Urithiru).

The Sibling can pull it directly from the Spiritual Realm. In theory The Nightwatcher can do the same for Lifelight and had Retribution not destroyed the Stormfather, then he would be able to pull in Stormlight. With his Honorblade Ishar can probably still open a Perpendicularity and pull Stormlight from the Spiritual Realm.

Well more and more it seems the Vessel of Adonalsium was a man who was killed and separated from the Power. Then the Power was splintered into 16 parts; The Shards.

The "obvious" choice is Adonalsium, though that could definitely be a red herring.

The Sleepless Epigraph seems to indicate the Sleepless going there is a new development:

@Treamayne that is fair, I may have jumped the gun from speculation, though it makes a lot more sense to me for Odium to have invested Roshar there because Duralumin from the moon would block Honor and Cultivation from seeing his Perpendicularity rather than it being a Godmetal. Presumably, Tanavast would have been able to identify a Godmetal while he would not be able to see Aluminum/Duralumin clearly. Assuming Rayse's Perpendicularity was already there at the time of the clash, then something else to consider is when Odium & Honor had clashed over Stormseat the Cymatic Rhythm of War would have echoed with the Rhythm of Odium coming from the Perpendicularity beneath. The Pattern the Plains shattered into is very likely the Cymatic Rhythm Of War similar to the other patterns we saw for the Dawncities from Kabsal and then Navani's experiments. To me this indicates Retribution investiture/The Rhythm of War.

The clash was not nearly as devastating because Preservation tries to Preserve. By its nature it offset a lot of the damage. @DiePie beat me to it. Also to add to the part about the Moon; The 4th Moon was likely made of Duralumin (not Aluminum it was something more) it would indeed block some of the Investiture from Odium & Honor's clash.