Larry, I was kidding. I'm not big on the idea of keeping an entire selection of parts for every bike I purchase. Though I do have them, I believe having all that stuff on hand in case there's some sort of break down is really big time overkill. Many components, like the throttle, the motor itself, brake levers, and the PAS sensor, ARE able to be checked with a meter. Things like the display and the controller are where things start getting complicated. I could see the paranoid keeping a set of those on hand. The rest of us though, would likely do well to wait until we had some sort of unexplainable issue going on, where we could then order out a set, and would likely reap the benefit of knowing we had the latest and greatest software/firmware updates included in the purchase price. That's my opinion anyway....
Absolute worst case? You could do something similar to what I did very reasonably. A kit that includes a display, a controller, PAS sensor, brake handles, all with matching connectors, is maybe somewhere around 150 or less. All you would have to do is adapt the 3 wires coming from your motor to the 3 coming from the controller. Everything else is plug and play.