I'd suggest you take a look at those "blow up's" of the Riquimbili's in "The Taveren". Most of those use a welded in place jack shaft where the small secondary front sprocket is fixed behind the 12" primary vbelt drive. If the motor has a 4" pully (preferably with a centrifigal clutch) then that will set you up rather well. That way your primary is a rubber belt and the secondary to the rear axle is a sprocket chain. Your slippage will be with the clutch and rubber belt primary which would be easy to service and repair or replace belts on.
Your braking may be best accomplished with hand brakes that grip the rims so the axle can be dedicated to the secondary drive chain. Otherwise you'll have to find a drive chev to bolt to the spokes and as yet I don't know where you'd get that.
As for the externals, lights, signals etc...I'd suggest getting the bike running and dependable first before anything else. If it looks like it's going to perform dependably, then yeah....invest in it. You'll find light kits in bicycle catelogs that have all that stuff as a bolt on. There's loads of customizing stuff out there if you wanna go full dresser. (chrome fenders, fiberglass rods with orange pennants, squirrels tails and all that)
I'm thinking that if you know some one with some welding equipment that you could canabalize a bent 10 speed bike to get the pedal crank out of it where you could make the jack shaft housing. If it's one of those bikes where the pedal levers dismount with tapered pins from the crank shaft, then that could be adapted under the motor mount and the small secondary/large primary pully wellded together on the working end of the ball bearing jack shaft. Then all ya gotta do is align the motor's centrifigal clutch up over the 12" pully. There should be clearance for the chain secondary drive under the motor.
If you'll study those Riquimbili photos (the links posted show large clear blow-up's in the thread below)