A rear geared hub drive would fit a standard 130 mm fork width, but you would probably lose any sprocket ratios over 7. I could never find a 14-32 7 speed sprocket in stock though they are in the catalog. I ended putting on a front geared hub motor to get my 8 speed 11-32 sprocket back, but you can't do that with a front suspension. I like the Mac12t for high torque at lower speeds. Maximum 23 mph on road. May be hard to find, I looked a year before I found one. Don't climb 1000' in an hour with a geared hub motor. it could overheat and burn a winding. OTOH I cross >80 hills in my 30 mile commute, some up to 15% grade, but only 100' long.
Your options are limited on a battery mount. You have room for a dolphin pack under the center bar, but making steel clamps to go around that bar would be several hours work with tin cutters, drill, etc. Might tend to slip down, too. I don't know if you could drill a mount hole in that center bar. Depends on the material.
You could hang the battery off the handlebar & fender mount on the front, but that means you have to steer it. I tried that, didn't like it much on my rutted drive out at the summer camp. My battery now is hung on the front off the basket mounts welded into the frame of my cargo bike. No steering the battery.
Note torque sensing is supposed to be more controllable off road. You have to pop the crank off with a special puller and put an insert in there to sense the torque. I would not bother to put a PAS pickup on a bike like this. I didn't like PAS even on a Murray cruiser on road. The edge of road pavement on State hwy 3 is not good enough for 11 mph minimum. I use a throttle exclusively until it comes time to replace a crank (which it might be now, it is clicking every revolution & center bolt won't tighten more. )
