I can easily beat Lv11 with a Team arround 65 Althea, Beatrix, Billie and Micah.

Micah works realy good for that amount of enemies, but it's still random that she hits enough. (one shot if it hits, exept for the Elis)

I think the bigger problem will be, to get enough materials even if you can not fail the missions... the droprate of the arrow and heart item for the Maidens is just WAY to low. If lv12 do not drop them at a higher rate, then it's impossible to get both maidens, even if you play active(without refill your energy with gems.)

But at the end i think, Lv12 will be on a hard level, even for my team.