1) people answered...
2) I've heard having teams of all lvl 20s is enough but we wont know till its actually out.
3) I'd say focus on your 4/5*s now since you've gotten a decent base team already. I'd say get them to lvl 30 each if not higher (more for Orchid). You should probably start looking towards evolving some of them.

Another important thing is focusing on affection. Its crazy powerful for 4/5*s so if you haven't already I'd say run ?-4 of the event mission until you can 100% most of your 4*s. Since gifts are pretty hard to come by outside of event missions and the gift special quest is horrible outside of the 2 flower gems.