Hi bugnut, welcome to the forum from Dallas. You can answer a lot of your questions from just browsing the forum.
You have zeroed in on one of the most important aspects of the build, the rear drive. What comes stock will work, but it's very labor intensive to install. There are several different types of sprocket adapters available for different applications. One of them will work with 3 speed hubs. Also you can get one for a single speed coaster brake, and another one is for disk brake hubs.
Have fun with your build and try not to get in too big a hurry.