Going off advice given to my design, and the veiws i know others share I'd say it seems to have the right things in the right places pretty much.

Critisism: flip the stepper motor and mount it on the back then use a belt and pulley system. This will reduce resonance, as well as other things? (correct me)
Perhaps also mount the ball nut inline with the rails, might help give greater travel in x?

Finally, ignorance is getting the better of me, are you really from chernobyl?