Re: Peddling comfort?
I have only built one motorized bicycle (so far) which is not much compared to some others around here. I did weld a custom stretched frame though, since I knew the regular "large" (ha!) Worksman frame would be way too short to even hope to be comfortable.
With the frame I made, I didn't put on any separate footpegs, I just used the pedals as footrests as I assumed it'd be easiest and would work okay. What I found out when I started taking longer (2+ hour) rides was, it didn't. I didn't pedal at all, and yet one leg was always uncomfortable. You could spin the pedals to alter the leg positions, but all that seemed to do was make both legs uncomfortable.
I did use a cheap bobber motorcycle seat instead of a bike seat, and the motorcycle seat was really rather flat and not shaped to allow the rider's legs to pedal like a bicycle saddle is. I think the motorcycle seat was the better choice though, since I very rarely pedaled the bike at all. The main problem was that I hadn't made any good foot-rest locations.
If and when I build another motorized bicycle (and make the frame myself again) one mistake I will correct is putting one (maybe two) pairs of footpegs right where they will be the most comfortable, and then figure out where to stick the bottom-bracket/pedals afterward.
One future option is to use travel-bike pedals (that fold up) on the cranks, and then use flip-down minibike pedals welded onto the frame wherever you need them, even inside the diameter of the pedals' rotation. You could not pedal and have the footpegs extended at the same time, but then again, you wouldn't ever need to.
I will also say that if you wanted a bicycle that you could still pedal easily, then none of the common kits is really ideal. What I would build for that is a fork that could accept a rear wheel, and then build a chain-drive that used the front-mounted rear wheel's freewheel. That way the bicycle would always be able to coast forward normally (even if the engine was off) and you could also (pull-) start and shut-off the engine as you were in motion, while remaining in motion.
A lot of vintage bicycle engines (usually friction drives) were built this way for basically the same reasons, but nobody seems to be making kits for it now.