What kind of four stroke motor and transmission motor do you have?
And you definitely gotta step away from the rag joint set up. The clamp on to the spokes thing your probably have. you need an adapter that clamps on to the hub instead, pirates cycles and sportsman sell some.
And 14ga spokes on a motor bike is not enough, you at least need a 12ga spokes. You can find a beach cruiser wheel with steel rim and 12ga spokes easily for under 50 bucks
you can get a rear mtb wheel with a disk brake, you can mount sprockets in place of the the disk. Also a very good set up... I know Kings custom sprockets sells them.
The set up i have is a heavy duty break with a special adapter that threads onto the hub and is locked in place by a locking with a built in band brake.
And by the way Welcome to the forum!
P.s. were are you located in Cali ?