I’m really, really into this. Loads of great ideas. I think it’s absolutely necessary to introduce Palpatine throughout the trilogy, and a Snoke redub seems very sensible. I think FreezingTNT is right that ideally you’d be able to reuse existing dialogue, though that’s likely to be difficult, in which case your proposed alien dialogue with subs would be fine.

I don’t think Kylo needs to drop the ‘Kylo’ name though, especially since nobody uses ‘Darth’ for him in this. If you keep Kylo it’ll stay closest to canon.

This is a personal one, but instead of having Rey channel all Jedi at the end, have you considered keeping Luke and Leia alive until that point, and having their deaths coincide with Rey’s dual-wield defeat of Palpatine as they give her their power? The crawl in TROS could explain that Luke had chosen to stay on Ach-To to explore a solution in the force to Palpatine, while Leia stepped up to train Rey. That way her defeat of Palpatine is our three living Jedi versus the strongest Sith, as symbolised by the pair of sabers, and also IMO gives her a better claim to the ‘Skywalker’ title. It makes her powerful enough to defeat Palps without her being a Palpatine herself, and makes it far more personal to both Rey and the audience to have our two Skywalkers help her rather than just a mob of ghosts.