My all time favorite frames are cruisers, maybe because that's what I've grown up with. I've have had other frames, and built motorized bicycle on them. I had a thin steel frame and the down tube cracked in half. Aluminum isn't any better, in my opinion. Also the tubes crush too easily, so particular attention is needed.
So I stay away from them. You want a frame as close to a 75 degree "V", but you can work around that. Since the cruisers have a curved down tube, I find that a custom front mount is needed, as a engine out of the box won't last long. There are a number of options. Now the coaster brake, at first I had one but changed it for pad brakes, which is easy. Using the coaster set up.
HT with a coaster brake set up.
I recommend taking the sprocket and enlarging the axle hole, keeping the dust cap intact. Some cut the dust cap. Here is a video I made.
Whichever you decide to build, I know you will have a ball on it. To build one correctly, disregard the 2-3 hours they tell you that it can be built in.
Here are some recommendations I have for installing a China HT.