Welcome, and thanks for your support!
It seems like everyone (and their dogs) is calling their motorized bikes "Jessie James", so I found one of thousands to discuss...
There are many options for this kind of sprocket mount, but here are the ones I know of and have tried with opinions...
1) Bolted to the spokes.
This is by far the easiest option, but also the worst. All I can say is... don't bother.
2) Bolted to a disc brake hub.
This works well, and can take perhaps 2 or more horsepower. I did this by hand filing out a sprocket from a 1 piece crank...
3) Custom machined hub.
Best option for sure. With all the gas bike kits around, you can surely get one for under $50 from the many online sellers.
A proper sprocket hub with 36 spoke holes could easily take 4 or more horsepower on a decent 20 inch BMX rim.
Brad