A very nice assembly there, effective yet still simple enough for most people to try.

I personally don't think you need to worry too much about an extra bearing support, although I don't imagine there would be anything wrong with adding one. Your wheel currently sits quite close to the gearbox, similar to where it would be on a standard drill motor. The extra bearing supports were recommended because the threaded part of the output shaft, to which a wheel is normally screwed on, is much further out than usual and the shaft could have been more prone to bending, but you've minimised this issue with your design.