I am new to Forum , just joined yesterday, and am impressed on how much help and knowledge is accessable. You design looks great. My only comments are I prefer a steel subframe for weight and rigity. You may want to look at some of the Chinese machines (Ebay and the internet)for ideas such as the Jcut 6090B or DW-6015 machines . Theirs has a cast iron base and are very cheap to import. It is very cheap to build a 2/ 2-1/2" tubing frame to have a very rigid frame to mount your Aluminum components to. The top could be a 12ga. or so steel 48" x 96" plate with all the necessary mounting holes cut off a laser.
I dont quite understand your guide system but I would recommed using no less than 25mm sq. guide hardened rails and linear bearings . These are very cheap these days and I recommed
Automation Overstock, surplus automation equipment, overstock automation devices, manufacturer overruns, linear bearings, variable speed drives, circuit breakers, contactors, starters, relays . You wont believe their prices on Hiwin HD Rails.
If my comments dont make sense to you application its mainly because I am new to the current designs or CNC Routers. Good luck. Hubert, North Carolina