Re: thinking about a motorized bike for pedal assist
The in-frame 2 strokes add quite a bit of resistance when only pedaling. I would suggest a small (25-35cc) friction drive kit. You would be able to raise the motor from the tire at will so there would be no extra drag. I don't think there is much a reason to go with one of the popular China kits if you only want part time assist.
If you're good at building things, check out the DIY section, lots of people are using small weed whacker motors to build friction drive bikes.
Welcome to the forum.