Very nice looking product line you have.
My concern about use the 2X4 cross members is wrapage and twisting. Seems to me if you are building that caliber of a machine you may want to consider using steel tubing. I can visualize a pneumatic clamping system and pneumatic levelers.
I have been researching a water cooled spindle for one of my machines. Looking at a 1.5K spindle (all that's needed for me). Did you build your own VFD or was it purchased?
http://www.ebay.com/itm/230715508514...84.m1438.l2649 are pretty reasonable and may go that route.
BTW>>>> Welcome to the forum.