Steve your more then welcome mate, dont worry about your spindle just yet mate get everything else sorted out first. Like me you will pick up information and knowledge as you go. Also if you have a look on zapp's website you can get the ballscrews and 16mm rail all under one roof.

Kip its not my spindle, it was by cncdudz. My design was always 43mm ! Do you have a good source for the 20mm supported rail ?