I've got the weekend to put it together...
The bike has a geared coaster brake
Hi Steve, Welcome.
Don't give yourself a weekend to put your first build together bud, even you only plan to ever build that one.
They are not like an Ikea table kit.
At the very least you need to understand whats in play parts wise just to maintain it.
A geared coaster brake?
A model name would be helpful but I figure you mean a no gear bike you can pedal backwards for the back brake.
If it's a department store beach cruiser you may find that due to the gearing your only brake will barley stop you at 10 MPH.
With all the extra mass and inertia you get with a motor even at 10 MPH you NEED to put a lot of time into your braking as the bikes coaster rear brake only just won't due.
Buy a front rim brake, period.
Mount the lever on the throttle side.
If you want to improve the coaster brake, just change out the (usually) 18 tooth rear sprocket with a 20 tooth.
Besides the lower gearing giving you much more torque on the hub brake (enough to skid) it also makes it much easier to pedal up to start the motor.
Note that the downside of this is if you plan to pedal a lot, though easy to pedal, you have to do a lot of it to get anywhere.
That is really easy by the way, but if you don't want to mess with it or just use the coaster for a backup get a rim brake for the back too, and use a Teeter-Totter dual pull lever on the throttle side to operate both.
Unlike the dual pull levers where each cable hooks directly to the lever, the Teeter-Totter dual pull lever balances the pull force to each brake and works like this.
As you can see by my crude .gif animation of some pics of my ride with dual rim brakes, one brake needs more pull to engage force than the other, but the Teeter-Totter allows the front V-brake and back single side brake to work in unison with equal force.
Again, welcome, and I hope that gets you off on the right track ;-}
