Blah blah blah, Phoenix squad.
Sadly, CG dropped a clanger with the setup for new players. The only way to get decent toons is Phoenix, unless you bypass those and beeline straight for CLS (Commander Luke Skywalker, you'll pick up the abbreviations).
The issue with Phoenix is gear, which is why most people who aren't lunatics like myself get G8 and stop there. 8 is bad enough, believe me.
G8 Phoenix can *just* about do Thrawn at 7* but that sounded like hours of work, so I went ahead and geared my Phoenix up a little more and it was still painful. I'd wait until you start swimming in a few more resources until doing Phoenix and maybe go for a Wiggs team with some of the OG rebels (those can do Palp at least).
The game soon stops being any level of fun once you get locked down in a long farm like Phoenix.
You'll get Tarkin for free, you can soon knock out Stormtrooper, you can get palp with OG rebels, Vader will happen when he happens and maybe get Veers or somebody else to fill the 5th slot.
Now I'm saying the above mainly because the only answer anybody ever gives in these topics is Phoenix, I'm trying to provide alternatives which are much easier to gear than Phoenix. The synergy of Phoenix is insane though
I suppose you could farm Phoenix a bit to maybe 5* and get Thrawn that way, as a 5* Thrawn is nothing to sniff at.
Sadly Farmboy Luke is kind of a wasted toon slot really but he's needed for CLS, the other 4 are OK to great though. ST han, Old Ben, Leia and R2. CLS can solo the rancor which is the best raid for gear bar none (will help you with Phoenix), tank is pretty garbage, and STR is diabolically bad.
So there you go, an alternate route if you don't want to go the same way as everybody else. I didn't go that route myself but I kinda wish I did.