12 mph on a 10% slope is far more than I'll ever ask from this motor. And I'm giving more than 100W while pedaling, I'm not using e-bikes like scooters. Obviously, real life trials would give me the exact feeling about this motor's limits.
So, first thing I'll do is to change power connectors on those 3+2 (motor phase and battery wiring), probably I'll sold them. BTW, the controller is this one
https://www.greenbikekit.com/250w-24v-36v-electric-bicycle-hub-motor-controller-with-led-meter.html
It looks (and feels) cheap, maybe in the future I'll change it with something more robust and featured - 5-6V power output for frontlight - rearlight on a trekking bike is always a plus, for example. I have to stay under legal restrictions in Europe, 250W rated power and 25 km/h.
The suggestion to change chainring-cassette gearing is interesting. Although I'm not going to reach 30-40 km/h range speeds (wasn't my purpose with this bike), pedaling like Chip 'n' Dale is to be avoided, too. Maybe keeping 25-30 km/h as max speed with 36T chainring/12T cassette sprocket will keep pedaling frequency between human limits.
Thanks a lot for all your suggestions. If all the posts were so concise and useful, forums could be proposed for learning in schools.
P.S. I'll post my results, too, after some testing and experience gained.