After getting Lando to 7* yesterday and Biggs today I completed the final tier of the event in my first attempt with little trouble, though only 2 toons were left standing in the end. My squad was as follows:
ST Han, gear 10, lvl 80
Leia, gear 7, lvl 70
AA (L), gear 7, lvl 70
Lando, gear 8, lvl 72
Biggs, gear 6, lvl 61
So no, you don't need to max out everything.
Take out the guards first, then the emperor and finally Darth Vader. Save Ackbar's debuffing ability for when Vader does his aoe attack. All those DoTs will boost the healing.
(Edit: Only ST Han was fully modded, while the other 4 toons only had whatever left over 1*/2* mods)
