I am curious what changes you would make. I see there may be room for improvement on the z as well. For example, the v slot wheels on my z don't all spin when the z is moving up and down. I can freely spin the inside wheels. Also, I'd like to firm up the z towers a bit. I see some resonance waves in the side walls which I think is from the towers rocking.

Building the the parts first from ABS or PETG is a good way to prototype. I have used ABS with good results.