Hi irving
If i was making the handle assembly i would manufacture from one piece of ally with an interference fit for your two bearings. also make the 150mm length 22mm Dia & then you can fit some proper cycle handlebar covers.I bought that ring gear just to see if i could work out the gear form(probable modular) don't know if the required wheel size will mesh though as the mating components from the hub it came from are rather small.
Take care M8