Re: Coaster breaks
Yup! A coaster brake plus two rim brakes is a fine way to go. Good stopping power.
The only thing that I'd add is to watch that coaster brake and hub. Motorized bicycling seems to be harder on them than it is on a freewheel hub. No surprise, I guess. Coaster brake hubs are a bit more complex and they include a few parts that can easily get crushed.
I'd suggest you start looking right now for bikes with a single-speed hub in the garbage. So that you'll have some spare hub parts.
And take your hub apart (carefully) and put it back together (carefully). A few times, so that you'll know this stuff when you need it. Pack a bit of good grease in there while you're at it.
Carry cone wrenches and lock nut wrenches (11/16 or 17 mm, usually) in your tool kit. You don't want those cones backing off.
And you should clean and re-grease your hub often. With the change of seasons seems to be about right.
If this is new to you, then it might sound daunting. But it's not really all that hard.
And you want to be familiar with the parts inside that hub.