Looking good Ellis... like how your putting a lot of thought into everything =)

In regards to those motor shaft protectors... great idea, just make sure you get some full length sleeves/standoff tubes on those bolts if you can... will be much stronger if the base of the standoffs can press up against the motor casing rather than resting on the shaft bearing neck like you have now in the pic (will reduce unwanted sideways flex)

I'm assuming you have them where they currently are, because they are too large in external diameter to slide past the bearing neck, but if you get some longer standoffs, and use a grinder/dremel/flatfile... you'll be able to remove some material off of one side of the standoffs, so that they slide down to the motor case end.
Obviously you wouldn't need to file the whole side down, just the length that would need to pass the bearing neck on the motor casing.

Possibly overkill... but another thought might be to get a washer and a thrust bearing in between the gear face and the brass bushing you have there... then again it does look like you could be pressed for length on the protruding shaft *giggdy
so you could mill a larger hole in the brass bushing you have there, then lathe a brass collar that fits over the shaft but inside that recess in the end gear... then the thrust bearing could be cupped by your retainer and sit on the top face of the lathed brass sleeve.

If your gram counting and are wanting to be this meticulous, you could tack weld some needle bearing cartridges onto those steel plates you have holding the brass bushing instead...

food for thought, that my random 2 pence in anyways haha