[Al Skierkiewicz]

It looks like you have all the bases covered. I would look at the upper bearing being a little larger in diameter with a central hole for wiring big enough so as to allow power and control wiring. The lower bearing/followers are a good idea too. Remember though that using the chain and sprocket design raises the steering power demand and allows for objects to block the turning if they get caught between the outside of the wheel module and the robot frame. Tank steering is OK for changing orientation but is not need for normal driving. As always (after it is built) practice, practice, practice.
Good luck!