I just purchased a pair of Two Pi Tower kits, and want to make the cabinet using 13/16" marine plywood with 1/2" natural wood around the inner plywood box, on all sides plus a plinth or base for the tower.

My questions are:
1.- What inner dimensions should I respect in a Two Pi Tower box? The plans detail only outside dimensions of 46"x16"x13".
2.- The thicker or stiffier the baffle, the larger the port hole must be? Why is that?
3.- The "General Tips" file says "Remember, you can’t overbrace!". Does that mean I should use as many braces as possible? Or does that mean only to use enough bracing as recommended in the plans?