Building wheels..

You're on the right track. There are spoke calculators on the internet to help you determine what length spokes you need. While you are shopping for moped hubs, pick a rear one that has a driven sprocket already mounted. You can always change the size of the sprocket to what you want later. Then you have eliminated the need for a hub adapter for a sprocket which may be hard to find in a moped size and bound to be expensive. There are many different configurations for moped hubs, just look for one that satisfies your needs... pedal sprocket on the right side, engine driven sprocket on the left and drum brake built in. Oh, and 36 spokes as you said. The right hub may cost you less than a hub adapter would. Up front you want something beefy with most of your stopping power. I've heard people speak well of Honda hubs. Don't know offhand from what.
What Villiars engine are you using?
SB

job done:



these are 16" moped wheels, 36 spokes, drum brakes, with Pirelli ML75 tires.

mopeds and motorcycles use the actual rim diameter in inches, so a 16" wheel is the same as a 20" bicycle wheel. the pirelli's will fit on a bmx rim, and they're super cheap, too.

http://www.jcmotors.com/p-20819-pirelli-ml75-scooter-front-tire.aspx