I use the bushing as well as the adapter. To make a bushing is more tricky than to make an adapter. The adapter has the advantage that you can simply use different propellers.
If you have a tube from brass with an inner diameter of 4 mm and a shaft of 4 mm from metall that fits really good, I could try to modify the hull. Just tell me the outer diameter of the tube then.
In this case of course I also have also to modify the coupling.
Yes, you can take this controller but it is has no switch. So you can't use a switch. You will find controller with a switch only on special boat controllers.