Make sure that your scoundrel team can beat the highest tier of credit heist available to you. You will need those credits to develop your roster. Get your team ASAP. Chewie is strong enough at 5*. No need to upgrade him any more. Boba Fett is a favourite scoundrel (also great bountyhunter and pilot). Stormtrooper Han will be needed to unlock Commander Luke Skywalker at some point. Those 3 are all easy farms and can be your core on the team, while you have several options for the remaining 2 — but prioritize scoundrels that are also bountyhunters.
With a team of 5 rebels you will be able to unlock emperor palpatine. A team of 5 Phoenix (which are also rebels) will unlock Thrawn. A team of 5 empire toons (EP and Thrawn are also empire) will unlock R2D2.
When seeing your current roster:
Ackbar, KRU, Biggs, Vader and JC are all great pilots on great ships. I'd keep developing them.
Talia is great on a NS team (but weak anywhere else). Kylo Ren is strong with FO. Jyn is required to lead a Rogue One squad in TB. Dooku has his uses in end—game. Sidious is a niche character. I would postpone farming all these until later.