I do not monitor the temperature. I touched the motor after a half of an hour of riding at maximum speed and it feels quite hot. As far as I know the Innotrace X1 controller monitors the temperature and it limits the power when the motor is too hot. That 3000W power the controller delivers is...
I can live with loudness, clunkiness and inefficiency too as long as it works reliably and lasts lifetime.
I do not think you can do much about those things with big straight cut steel gears, that's the price for robustness.
If you are looking for low maintenance and longevity you have to use the biggest diameter rotors (220mm or 223mm?) and calipers with biggest contact area brake pads with sintered metal compound. Magura quad piston calipers offer probably the biggest brake pads.
I would pick the same frame again because of this is the only frame offers such big battery, big motor and looks very good at the same time.
By the way I did not mentioned here but you have to apply Loctite SF7471 primer and Loctite thread locker (probably red is more suitable) on the rear...
There is Optibike with such power. It looks like pretty good 2500W emtb with its own motor. There are also good frames for Bafang m620 motor you can turn to 3000W and equip with good components. Some sells complete emtb bikes with unleashed m620 motor and good components like Watt Wagons or...