My 2.01 cents
1) The storyline is Rebel RS, for the campaign.
2) Imps are definitely playable on multiplayer, and possably a mode like skirmish.
3) Yes I can see the sniper rifle + Jetpack Combo, and other things being common.
4) It is PSP only, so unless you xlink Kai you are going to play with your friends physically near you. If you don't like them using the jetpack just walk over and give him wegie, or dunk his PSP in coffee, whatever you want.
Don't know if Clones/Droids are playable, but There are scenes of Clone equipment. Then again it might just be old relics not meant to be in the game.
But I would love to be a nice ewok with a shotgun, fusion-cutter datpack. It might not be practical, but would be loads of fun. Its like GTA: Star Wars, only being shorter.