1. Backlash nearly always comes down to price. Only you can decide if you want to spend the extra time and money to reduce it.

2. Are you basing your calculations on the effiency corrected torque?
For a given pitch, the ballscrew will transmit nearly twice as much torque compared with the acme, which means you could drive the same table at the same force, but at twice the speed using the same motor.

2/3. Speed depends on how much torque you're willing to sacrifice. If you go for gearing (usually done via belt drive), then you can increase torque and resolution, but loose speed, or vice versa.
Plus I've seen it mentioned that you shouldn't rely on microstepping for positioning and you should only expect accuracy to the nearest full step.

4. Everything wears, but ballscrews should be minimal provided that they're well lubricated.


If you're unsure, then go cnc with the standard acme screws, and see how you get on. You can always convert to ball screws at a later date.