Hi
I used 1/2" sintra for my 2x2 table top. I created a T-slot table by running a keyhole router bit down the length of the sintra every 2" I then cut strips of 1/4" sintra and double sided taped them between the slots, then milled the 1/4" sintra flat. The keyhole bit only allows a 3/16" bolt, so I had to cut one direction, move over 1/16" and cut back to allow for 1/4" bolts to clamp with. I did this on a larger CNC machine, but it could be done on its own machine if the axis allows the bit to start and end past the table.
I built a vacuum system for a 4x8 table several years ago using 1x2 aluminum tube. I plugged the ends with sintra, built a manifold out of pvc pipe and ball valves, wrote a program to perforate the tubes with 1/4" holes, taped 1/4" sintra to the tubes, ran the program again with a 1/8" bit to perforate the sintra, and milled the whole thing flat. Worked well with a shop vac, and great with a regenerative blower. For 12" x 36" and balsa, I would use a shop vac and skip the manifold and valves.
You might have a problem getting double sided tape off balsa without breaking it, so I would recommend Anchor brand paper backed tape, which is like double sided masking tape. It holds well, and can be removed easily. Just don't get it wet
I seem to be running on a bit here, but I hope this gives you a few more ideas to pick from.
Steve