Interesting start. Unfortunately im on my cell phone at the moment so havent followed most of your links.

A couple of things:

1. The stepper drives you have are notorious with respect to their engineering. It is highly likely they will cause you trouble.

2. Aluminum leaves a lot to be desired as a linear ail material. In one of your posts i saw the word "bootstrap" so maybe you are aware if this. Given that some designs are better than others.

3. On a low cost build keep an eye on rigidity, a sloppy design or construction methods will resilt in a poor performing machine. I havent checked out the design you have selected but many of the examples floating about the net seemed to have ignored this. Dont be affraid to reinforce things. In one of your pictures you have cut a bunch of 2" wide slats, that worries me a lot.