I'm a huge Top Gun fan and I can't wait to see the new movie too. It's a shame it was put back to December but, well, it is what it is.
As for the cast/characters for the new movie, here's what I was able to find out but this isn't confirmed as yet....
Tom Cruise as Captain Pete "Maverick" Mitchell, a test pilot and flight instructor.
Jon Hamm as Vice Admiral Sam "Merlin" Wells, who replaces Tim Robbins from the first film. (Merlin became Vice Admiral?)
Ed Harris as Rick "Jester" Heatherly, a rear admiral, who is Maverick's superior. The role was originally played by Michael Ironside in the first film. (So Ed harris is going to be Jester in Top Gun 2?)
Val Kilmer as Admiral Tom "Iceman" Kazansky, a fellow instructor and friend/former rival of Maverick. Now a four-star admiral and in charge of Naval Operations.
Charles Parnell as Rear Admiral Marcus "Sundown" Williams, who is Maverick's old colleague in the old-time and once served as Maverick's RIO after Goose's death. The role was originally played by Clarence Gilyard in the first film. (So sundown became a Rear Admiral?)
Jake Picking as Ron "Slider" Kerner. The role was originally played by Rick Rossovich in the first film. (another strange one when you look at how old the actor is
https://www.imdb.com/name/nm4917623/mediaviewer/rm2113176577)
Raymond Lee as Commander Mike "Viper" Metcalf. The role was originally played by Tom Skerritt in the first film. (This is another strange one as the actor doesn't look old enough to play Viper in the new film. He also looks nothing like him. One can only assume the makeup dept is very good).
Lyliana Wray as Charlotte "Charlie" Blackwood (Yes, this is news to me too. Although I can't see how this person fits in with playing Charlie as the actress is very young. She has been Tweeting a lot about Top Gun 2 though.)
Jean Louisa Kelly as Carole Bradshaw, Goose's widowed wife, and Rooster's mother. Kelly replaces Meg Ryan who played Carole in the first film.