HI
We have a total ban on motored bikes as well and I even weigh more than you at 350lb. My ride to work is 30k's each way on relativly flat ground but do have a few very busy intersections where I must move with the traffic.
I started out with a Staton drive and a Honda 35cc and found that very reliable but a little slow in take off. Then I put on the Honda 50cc and the ride to work was heaps better with plenty of top speed and fast off at the lights. Now I have moved to a NuVincci drive and put the 35cc back on and I get a little less top speed but a little better take off.
My advice is if it's a single speed you need a 50cc and with your weight I would be looking at a drive that does not fix the drive sproket to your spokes as I have broken many with a hub sproket.
Good luck
Alex