Summary

This is a customized (larger) version of http://www.thingiverse.com/thing:1734496 .

It uses 608 bearings (22 mm outside diameter), while http://www.thingiverse.com/thing:1734496 uses 10 mm outside diameter bearings.

For the shaft, I would use 8 mm in precision rod (the one you use for your printer). To block the gears on the shaft, check my 'steel version rod' design - http://www.thingiverse.com/thing:1705088