This is what seems to work best for me. There is two versions.
Chewie - leader
Jc - or 4* Lea
Phasma - leader
First off I am p2p I've bought the Kylo pack and crystals once. However I believe all the character I use are f2p.
I am lvl 62 and with some tweaking and a "death squad" I can seem to complete all challenges and GW. I'm hovering around 200 in arena.
The basics to my team are to use Poe turn one taunt for two turns, followed by a Chewie taunt turn three. If timed right this leaves your opponent only one turn to target any other team member turn five. I find that controlling your opponents target to be the biggest advantage in the game.
I will usually use talias heal turn four followed by lumi. This usually restores the team to full health turn four-five and then the taunting can begin again while I eliminate the opponents at will.
The reason I have two options are for GW. Sometimes for no reason I can figure out swapping in Phasma makes all the difference. Same for Lea for JC however I imagine the swapped characters can change as long as the basic taunt-taunt heal is in place.