There are some pretty good DiY controller designs that are working with the Leaf motor. This one is the one I will be using...
You might be able to, but you'd likely have to keep the stock battery and BMS too, neither of which I am using.Can you use the stock Leaf inverter, if you keep the stock throttle and sensors? I don't see why it wouldn't work, as long as the inverter thinks it's still in the original car.... plus this way, you can keep your regen.