Seeing as how you've only got so much to work with and you'll probably have multiple days to try different combos here's what I'd say might work well:
Teebo (L), Rex, Phasma, Tarkin, Fives - TMR team, Rex and Teebo keep TM contained, Teebo lead will grant stealth and suppress the number of counter attacks. Tarkin has an AOE TMR and can apply offense down to keep everyone alive longer. Use Rex's tenacity up whenever the main cannon is getting close to taking a turn. Phasma for AOE speed down, Victory March can grant everyone 50% TM so you can bump Teebo/Rex to 100% tm if you need them to reduce bosses TM. Fives for Assist attack and hoping Rex/Teebo gets called.
Teebo (L), TFP, Tarkin, RG, Lumi - Teebo (L) needs to be Omega'd for this to have a chance. Use Tarkin to apply Offense down to all of the droids. The 50% chance to gain 25% TM from Teebo's leader ability combined with TFP's unique where he gains 10% TM for each debuffed enemy at the end of his turn can give him up to 95% TM after each turn. RG is there to buff the team and taunt if everyone gets too low, most of your DPS will be coming straight from TFP though. Use Lumi for a backup buff with her heal if RG is ability blocked or whatnot before the cannon fires. Also you can use her to heal anyone who drops below 50% health to keep them alive longer. This technique is better with more tanks, but this team should do decent, also Teebo's lead isn't quite ideal for it as it's a little random as to whether or not you get the extra TM at the end.
Boba (L), Biggs, Ig-88, Ig-86, GS. - Idea of this team is Boba's lead is great for crits. Just load these guys up with crit damage and crit chance and just call assist attacks all day on the Rocket droid until the cannon slowly takes you out one by one (Hey it might shoot Boba a bunch and he'll revive). You don't have that many 6/7* characters that can apply teamwide buffs for multiple turns so you're just gonna have to accept that for now. The only options you have in that regard are RG, Lumi and Rex. (I don't count Phasma as that timing is veryyyyyy difficult). So you're just gonna have to deal damage quick and fast and this team is ideal for that.
Those are the main teams I'd suggest trying out from what you've got currently.