Ayleid worship - Did the Ayleids really worship Magnus? And what was he renown for?
Magnus is the reason why magic exists. He created the sun, a hole in Mundus which leads to Aetherius.
Ayleid architecture - Why are pretty much all Ayleid ruins underground? And why are a majority of them part tomb or catacomb like?
The stuff not under ground was razed, I guess.
Magnus - Did he create schematics and diagrams for the design of Mundus? If so, could it be safe to assume he didn't create those on regular parachment? Does Magnus ever communicate with Mundus or the inhibatants of Mundus? Such as the Ayleids or Galerion.
Magnus did created the plans of Mundus and since the material world didn't exist back then, there was no regular parachment. You have to think more abstract.
Ceporah Tower - Any idea who created it? Were documents stored here before the arrival of the Aldmer?
Wasn't that the Sload? I could mix something up here.
Ayleid migration - Did the Ayleids migrate from Summerset Isle? Or are they really descendants of the Aldmer?
They came from Summerset I think, and they remained even vassals of the kings of Summerset, officially. Yet not practically.
St. Alessia's Rebellion - Would it be safe to assume that the Ayleids knew or had suspicions of Alessia's rebellion?
It was Ayleid civil war back then. Some Ayleid city states even helped her.
Before the rebellion broke out, I guess nobody cared for the slaves because of the war.