5+5 Gwen for next arena season

Yes

odd numbered merge levels round down to the nearest even number for scoring purposes.

I’ll be honest, probably not. Unless you get an insane run with every kill going to Gwen and at least 750 on every run as baseline, you shouldn’t even bother. With a legendary hero as a bonus these next couple weeks it only pushes the ceiling higher as well. I can tell you from experience that 3780 isn’t enough during these weeks, so if you feel up to the challenge, aim for 3800. Good luck!