Great question, but unfortunately a dually won't work properly on a Softgloss with wheel scrubs. I think it would squeeze in there, but it would have to be perfectly straight, so most likely you would have a lot of damage. I like them too, but to wash duallies, you are probably better off with the on-board tire chemical sprayer with the high pressure option. It has a spinner that does a great job.
If you do the wheel scrub option, it wouldn't be too hard to get to the motor. Just drop the air to the machine, pull on the assembly until it's fully extended, and you have easy access.
For the drive wheel? Usually I would recommend doing wheels and tracks at the same time, and rotating the track every 10-15,000 washes. If you rotate it regularly, it helps to prevent he grooves that eventually wear the wheel out. Most sites can get 65-75K washes out of a set of wheels before needing to replace them. Some less, but it depends on how it's maintained. The hardest part of wheel replacement is pulling off the drive reducers. If you can drive out the keystock first, you can usually use a pry bar to remove those. After that, it's easy. Just jack the machine up a few inches, and unbolt the pillow block bearings from the frame of the machine. The wheels come right off as an assembly with the bearings. Install the same way. If things come apart easily, it takes maybe 3 hours to do the machine max.