What can I say - I found it hard. Very hard. I'd been dropping zetas and farming those murderbears single-mindedly. Unlocked him at 5* this morning. Was happy.
Tried the final mission to unlock him at 7*...got smashed. Tried again - got smashed. Again - got smashed.
I was very unhappy.
Put on Arena mods - smashed. Auto-assigned - smashed. Read a guide - smashed.
Was very, very close to walking away from the game for good. Why bother anymore after all that effort? Looked at another guide...reshuffled mods...basically as much speed as humanly possible. Read a bit more about getting the perfect start - and realised that is the key. If you lose two Ewoks and Chewie gets stealthed in the first wave then end it. Start again. You will not win. If you lose one Ewok that's ok, if Chewie is not stealthed. If you lose no Ewoks and Chewie isn't steathed - that's what you want and need.
I got it. Perfect.
In a nutshell you want to be hitting Chewie as much as possible, get rid of him. Except old Beardo rebel dude is going to keep taunting. SO - you need to work methodically - remove taunt, hit Chewie as much as you can (which won't be much), hit Beardo (nobody else you can hit) and eventually remove his taunt and put a few on Chewie. This is slow going...but, eventually and hopefully (if he's not put too many Wookie shots on you) he will go down.
Once he's down there's a little pressure off. He's the main attacker...now you have to repeat the above but between Beardo and Han. Few shots on Han, Beardo taunts, hit him, eventually remove his taunt and back to a few shots on Han. Slow and steady...the pressure is less now Chewie is not about.
Once Han is down? Pressure's off! Stick it on auto and make tea if you like lol. Between Leia, R2 and C3, none of them are going to cause you any significant problems. Get rid of Leia and then R2/C3 in whatever order you want.
And it's done. It's a marathon not a sprint. Takes some logic, patience, method and, of course, luck for that perfect start. BUT - once Chewie is down you can breathe easier. Once Han is down you can relax- you'll be fine.
Good luck, I hope you get him