From what I've seen, in the past games, some of the party members shared roles. For instance, in both games we had:
- A mentor figure
- A scoundrel
- A wookie
- T3, HK-47 and Canderous
I guess they should keep those roles the same (Perhaps without Canderous). I think that the droids should be in the game, since they're usually popular characters, and the game wouldn't feel the same without them.
As for new characters, I think it'd be cool to have a sith as a master, since we've had a LS'er and a neutral teacher. It'd also work to inform us about the enemy, since we know pretty much nothing about them. Aside from that, I have no other ideas. I was thinking a female mandalorian would be nice as a love interest, with her taking off the helmet once you get enough influence or something. I don't know.