I'm working on the film. Most of the stuff floating around is either bs or made-up from chunks from MSW and such. Some of it is 100% on-point or really close, but those plot leaks that pop up daily are mostly BS. Film's way bigger than you think.
I'll try to answer questions you send my way, as I'm not in a position where I know everything going on.
How does Palpatine return?
why are you gay?
Time travel. Yes or no?
what toilet paper do you prefer
He appears as an evil Force ghost near the end of the film in the Death Star II debris (think of Darth Bane in TCW). He became one with the Force after supposedly dying at the end of ROTJ, but his "spirit form" isn't as strong as Yoda's, Obi-Wan's... So he pretty much influenced Snoke for years (not full possession). He can manifest only near where he died.
No. People should stop paying attention to RLM's dumb theory or leaning into Abrams' love for time travel sheanigans. This is straightforward.
Any Anakin/Darth Vader reference?
how much is luke in it and what does he do, literally all I care about
Kylo still wants to be like grandpa, and keeps meditating before his mask. We also get to hear Hayden's voice trying to bring him back to the Light, much like Ewan talking to Rey in TFA. Don't know if he appears as a Force ghost at the end, most people working on this don't know shit about the final scene and everyone signed an additional NDA. There are rumors about literally every good guy Force ghost being present there, but don't take my word for it.