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?

Bracing is important in that it keeps panel vibrations to a minimum. It is important that the cabinet not add sound of its own, and you should be able to strike the cabinet with your knuckles and not hear a resonant "drum head" sound. That said, the tower two π cabinet works very well with two sets of braces, one a third of the way up and another a third of the way down. They should be cross braces or window braces and they should double as a place to hang partitioning pieces of insulation across the cross-section of the cabinet. You want insulation to line the top, one side and the front (up to the woofer) and then you want two pieces of insulation to span the cross-section, resting on the braces. This breaks the cabinet into three partitions, and midrange energy cannot pass through, only bass. The cross-section insulation impedes standing waves from setting up inside the cabinet.

Should I flange the port hole on one or both sides using a router bit? Would that change the lenght required for the right Helmholz frequency?