Nice ideas, but i have serious doubts about using the 2.2kw spindle as a power source for this type of setup. The bearings are poor and won't take the constant side-load of a belt, torque at lower speeds is terrible as well. I looked into ATC stuff recently on my Bridgeport conversion and gave up as it was beyond difficult - I need an ATC that can handle 24k + but at those rpm's everything needs proper balancing which is beyond the home shop.

I would go for a BT30 spindle, definitely not R8 in any case.