I'm 3* cleared up to 9-4, been mostly getting manyu's for a while now though to improve the team.

I balance my teams to have close power and speed - as well as I keep one of each attack type in each group.

I only have 1 lvl 50, the rest are mostly 30's and a few mid-20's, so my teams aren't super-powerful or anything, but they generally aren't dying on me save for the Advanced daily stages, and even then, I still clear.