Adaptive F2P Guide

However that debuff removal has a cooldown of 4 turns and can be blocked (ability). Doesn't sound that effective against Vader+Boba?

Rex is a speed type, slightly slower than Boba. You have to mod him for speed and protection since his health is very low. He is mainly used as a leader and best with a supportive tank to soak up some dmg. Him and STH work great together since they both manipulate TM very well. He has to go first (or second if TFP is faster) and apply tenacity up, it's a 3 turn buff, so 4 turn CD doesn't hurt here.

Droids with JE and Nebit, nice! Maybe JE to be farmed in guild store before Rex?

For sure, but not before Rex. He can be good on his own, JE needs droid squad to function properly and you won't have them early on.

Tarkin and Mace 5 stars is only one star more than you get for free. Maybe worth it but I have put all my ship building mats on Ackbar's ship, so the other two are lvl1. How did you do it?

My ships are all 70-71lvl, not higher. Strugling here as well. However Tarkin is 60lvl, because of his challenges, wanted to 3* them to sim easily. It will be even more important on zeta challenge. Not saying you need to star him, but at least gear him and level up ship. I can't predict that zeta challenge strength, as well as how hard 75lvl challenges are, so guessing a bit here.

Also a 5 star Yoda cannot be used in raid, so I would need a 6* Mace. And I don't think Mace is worth it.

True, not worth it. However Yoda is not needed except for heroic AAT raid. You won't use him anywhere else. With that being said, you won't have any chance there w/o anakin and IGD. And those are a pain to farm, so Yoda isn't needed as fast as one would think. Was thinking more about unlocking defence mod challenges earlier, so 5* Windu is mandatory, but can be omitted if you're not in a hurry.