The motor I have now can go up to 55km/h and with my XTR rim brakes I'm able to stop very quickly, so I'm not overly worried about being able to stop. The front will be disc, but the back will have to be rim for now, as the frame doesn't have the mounts on the back. I would have to get an adaptor.
I was going to switch the casset from my current back wheel, to the motor. However, it would see I won't be able to do that. I have a bike cassette, and not a freewheel.