If you go with powerfull 12S ESC i guess you will more fly then ride … NICE
A friend of mine goes with 3D printed Wheelpulleys, they dont hold up bad. He had to replace from time to time but overall he is happy with it!
I understand your concerns that its expensive. But CNC work is expensive except in big numbers of production. And actually the E-MTB Market is to small to start a production of 500 units (-: i even cant afford the raw material for this. Cheers