Like many others, I, too, share in the opinion that we don't need anymore new main characters to focus on. I don't mind a few new secondary characters, but I want to see more plot advancement on our main characters in this season (for the record, I consider Mulan and Aurora main characters since we spent 1/2 of Season 2 with them). Give the secondary characters their 1-3 episode arc, then bow them out gracefully.
If they're going to continue to run through flashback-o-rama, then believe in "less is more". The flashbacks need to be plot advancing as well as character building, not just one or the other. So far, they've done alright with this, but I hope they don't slip back into old habits.