Use 36V battery always. You need a certain power, say 800 Wats. Then the lower Voltage your set up is, the higher current you have. Heat problem come inavoitablly. I saw people buy 14V battery from Hobby King. That is something I don’t understand, how big current you want? Why not increase the Volts instead?
Use Chinese ESC. For 35 USD you can get many good speed controller with Regenarative Braking system. And they work just fine. And come with Decent Remote usually. I never used a VESC before, but, I am quite pleased with ESCs I got.
Try some hub motors. Belt motor is more powerful. Yes, at a lower efficiency. And much energy wasted on belt torque transfer. Same battery, less range. And powerful hub motors can also reach speed 35 KMH. Hub motor with 10C battery also reach high speed up hill. Less noice, and better water proof.