How much travel are you hoping to have on the Z-axis? I think the spacing of the linear bearings on the Z axis looks a bit close at the moment. I'd extend those triangular pieces on the side of the Z-axis up to the top of that sheet - it should stiffen it a lot. If you don't then I think that the sheet of MDF will flex too much, resulting in poor accuracy.

What pitch screws are you intending to use? You'll struggle to get a good feedrate with those motors on only 24v. Their inductance is too high. They work well on 70V though...

Here's a drawing in solid edge of the motor you're using...might find it useful! You should be able to open it in solid works, if not let me know and I'll convert it.

Astrosyn 1Nm Size23.zip