Hi, at 70% finished build all you want is some admiration of the design.....it's too late now for advice or criticism on the practicality of the design......perhaps for the record you could post a few pics of the build if you have them and discuss the merits of why you did it that way etc etc.
Just for openers.......12" X 12" X 12"....that's a CNC gantry router configuration.....routers are not generally ideal designs for cutting steel..... the 12" Z axis height makes the proportions of the rest out of wack.......a 12" height under the gantry means with an X and Y area of 12" X 12" your side supports will be a bit "leggy".
If you go to a moving table design you can make the side supports massive to stop deflection, but that still means the Z axis hang down below the beam will be prone to deflection.
For a table area of 12" X 12" you "should" have a Z axis clearance under the crossbeam of 8" approx......just my opinion.
A column milling machine with 12" X and Z axes would be way out of proportion with the Y axis at 12" due to the massive overhang that the head needs to cover this dimension.
Ian.