(Part 2) I'm thinking of replacing all the Latin lonewords with ones from Valyrian. I haven't learned it on Duolingo yet, though. So maybe the First Men had a very Germanic language. The Andals had originally one that mixed with that of their Valyrian neighbours, making words like chivalry a thing. I'm still a bit of a language noob so idk.
Honestly, I think you’re right on with this (Common being a conlang that has, say, English phonology). And yes, I think it would be ideal to replace Latinate words with Valyrian words even in the English that gets used in the series. I know that would never happen, but still, it’d be cool.