Re: which engine?
Hi Mechanickid, welcome. For a kit, go with one of the many dealers here who have been doing it for a wile. Many folks fall in love with the concept and open a web page and it can be hard to figure out the pros from the hobbiesists. (LOL, sp) The kits from China are what they are. Amazining lil motors that are over taxed and do a great job. They can do around 30 mph but cruise happily at around 20. I weigh 165 and easily go up hill at around 15 with out peddling. On a steep hill I can do 30 with.
I get around 133 MPG on the bike I ride the most, but live in a very flat area.
There is a review of dealers here, but I could not find the link 4U. (a lil help?) But if I could be so bold as to suggest, read up on it b4 you buy. not that $200 is a vast amount of cash, but it is still $200. Thatsdax is great and bluecoller is as well. But ask around and find what works for you.
Great to meet you and post pics!