Two questions:
The lava planet where Vader’s castle resides… did it say Mustafar at any point?
Any idea who Vader’s hooded receptionist was? Someone from the EU?
1.) It didn’t say so in the movie, but I believe it’s confirmed in one of the reference books that came out with the movie. The visual dictionary and/or The Art of Rogue One, I think.
2.) I think he’s supposed to be one of the Emperor’s buddies with the goofy hats from ROTJ.
Well, it’s almost certainly the planet where Vader and Kenobi dueled. In current SW canon, that’s Mustafar. In other SW universes, however…