Hiya Hood,
I'm not 100% certain now, I won't be doing anything until I have the frame for the Z axis machined up and assembled, it might just be that it "seems" too big at present, time will tell on that one.
I can't re-read the whole thread but my guess is you would throw in a servo and go direct drive?
As for the X & Y motor support plates, what thickness ally here - 10mm, 12mm, 15mm ??