To avoid a coaster brake you'll probably want a multi-speed cruiser- then you have the cantilever handbrake fittings on the frame- You'll want to get a dual handle brake lever, to make life easier and safer while also fiddling with a clutch handle- about $15- at vendors here and on ebay.
I started with a Micargi 7 speed Panther- I think it was about $150 shipped a couple of years ago- the great thing about the Micargi is that it has an asian hub whose diameter exactly fits our motor sprockets, and even a ridge stop to keep the sprocket alligned and the correct length from the spokes- Schwinns these days have a high quality alloy hub, but it slants toward the spokes- the sprocket fits over it but it has to be supported solely by a rag joint or optional adapter
still have to use the rag joint to attach to my steel hub, but it's the next best thing besides a hub adapter or modifying a flip/flop hub to attach the sprock directly
The other great thing about a derailleur is that it acts as a chain tensioner for the pedal chain- so that it's easier to avoid using a chain tensioner on the motor chain- more reliable and much less weight- and a cruiser frame gives enough clearance usually otherwise- a mountain bike frame less, and a roadbike can have chain clearance nightmares.
The front shock fork was a later addition, and really helps smooth the ride, with a shock seat post added later as well. As a former racing cyclist, I have my seat set up, and it's a great peddling bike as well as a motorbike.