1. Based on one example of a rear motor that a friend tested and hearsay from a German guy that fitted some to his bikes, but that was nearly a year ago. Keyde may have sorted all the problems. If you buy direct from Keyde, the motors are covered by three years warranty, but I don't know the practicalities of how that works
2. Yes, you just have to get the number of holes in the motor and rim to match.
Jerrysimon fitted a front version to one of his Bromptons, and I don't think he had any problems. I think they only work with pedal assist. There is a throttle option, but it only works with pedalling.