Hi!
Consider to go 8“ instead of changing the gearing so much 66/15 with 8“ on 12s should be a good compromise. If you are a speed freak than probably no, but that gearing should be good with 8“.
In the case or on the pcb? The temp on the pcb is important. I doubt that any 4.12hw can run that cool with this settings. I assume you didn’t ride average 15km/h flat road all the time.
Before you go 4wd, please spend some time over here
Your battery pack doesn’t look very safe to be honest. There quite some points I would suggest to redo and I haven’t seen the full pack yet.