1. Timeline- Rogue one will be a film detailing the events of how the rebels maintained the layout of the death star right before episode 4 A New Hope. In other words it takes place in between episode 3 and 4.
2. Darth Vader's involvement- Darth Vader will be featured in this film but Disney has stated that he will not be involved in combat very much. Disney wishes to try and excluded the force from the film so that they can create more of a WAR type feel to the movie.
3. No Jedi- Because the force will not be the main focus of the film, the film will not be featuring any full fledged Jedi. However, it may feature a few force sensitive characters like the Donny Yen from the trailer character and maybe another.
4. It is not a sequel to episode 7- you may think that this is obvious but I can't tell you enough how many people still get this film confused with episode 8. This film is not episode 8, which will be coming out Christmas 2017.
5. This movie will be apart of the Star Wars Anthology series- Most people do not know about the Star Wars Anthology Series or don't really know what it is. The anthology series is a separate series from the main series which will strictly focus on the Skywalker family. The Anthology series will tell stories that are separate from that series. Another Anthology movie that are in the works is the Young Han Solo film which is set to tell the origin story of Han Solo. Young Han Solo will be directed by Phil Lord and Christopher Miller and will star Alden Ehrenreich as Han Solo.