I can see this going in several ways, but what I would like to see:
Mitsuki needs to establish herself as the band leader (the front person is not necessarily the leader, think Miku from Band-Maid for a Japanese band or Steve Harris from Iron Maiden for a Western band).
However, as an introvert (despite coming out of her shell a lot) I don't think she will do this off her own bat. Therefore Aya will need to step in, in some way.
Hime could also play a part, which I would love to see.
The course of music doesn't always run smoothly, lets not forget that when The Police were recording Synchronisty they hated each other so much that they recorded their parts in separate rooms.