The next weak spot was that we were relying on the motor's bearings to take thrust forces being transferred back down the ballscrew. This works up to a point (although it puts some stresses on them that will shorten their life), but once you exceed a certain amount they will push back and forth about 1/8". Most solve this by having a mounting block with thrust bearings holding the ballscrew end, and then using a spider coupler between the motor and the ballscew to sort for misalignment.
And that would probably be prefereable, but I didn't design for it and had to get creative. So above you can see one end of my motor (fortunately it has shafts on both ends) with a stop I lathed out holding a thrust bearing against the motor casing. There is another one on the other side doing the same thing, trapping the shaft in place. This was actually completely effective, and likely how I will do things in the future too. It saves on parts so long as you have some alignment adjust-ability in your motor and/or ballnut mounts.