had to look it up but the bothans were involved with the theft of the 2nd death star plans. not sure about the first. because the line about bothans getting the plans is spoken by mon mothma in return of the jedi. Star Wars: Episode VI - Return of the Jedi (1983) Mon Mothma: Many Bothans died to bring us this information. well not the plans but the information on where it was, status and palps being there. i just hope with this they don't have anyone starting rogue squadron because that is a luke skywalker thing. personally i think episodes 7, 8 and 9 will all end up being "just ok" while their spinoff stories (rogue one, the young han solo one and i think another is supposed to be a boba fett one? maybe?) will be far more popular. but rogue one looks awesome. and way better than episode 7. also i love how disney is slowly bringing stuff in form the expanded universe/legends books. like the qausar fire carrier which has only been mentioned in the legends books is now canon because it showed up in Rebels. i think most of what we'll see from legends though is ships and equipment and symbols (like the mandalorian flag in episode 7. i don't think that was ever in any movie.) but not many of the characters from legends.
maybe that's why the lead is in an imperial uniform at the end. she ends up switching sides to the forces of order and justice.
No, brand new character. People are guessing she may be loosely based on Jan Ors, a character that was in the EU.