What sort of problems did you get with Trapezoidal screws, as I was going to use them on all axis 16mm.
As much as I would like ballscrew, it just want work with my budget just now.
Im looking at x=1200mm, y=900mm, z=300mm ( I may drop each axis down by 100mm )
nema23 motors x 4, tb6560 drivers x 4 (stand alone drivers) and PSU ( upgrade to G450 soon )
Cad software I have is Autocad, google sketchup and draftsight.
From all the reading I have done on Z-axis, I think yours will work best for me.
jamie