Z-Axis design and advice

Good day all.

I am now starting to look at moving away from my DIY Built MDF & Plywood CNC Router/Mill.
It has been ok for small job's, and my pcb's, but I now want to move on to slighty bigger jobs, and also would like to start milling things like alu.

I have been looking on web sites, google, etc, at how other pepole have made there own z-axis.

Here is what I have come up with so far.

If you wish to view my design I have the SolidWorks files here: Click Me <1.2Mb.

I am not very good with SolidWorks, but I get there in the end, so the files might be some what messy.

I am looking to have it made from 20mm thick alu.
Will be using a TR16x4 leadscrew.

Any advice you can give me is grate.

Thanks for your time.

Best Regards.