RE: Do I need a balsa building board?
What's a T-Pin? Just kidding, I stopped using pins about 10 years ago. The main thing is a perfectly flat firm surface. I built my benches with 3/4" particle board, sanded and sealed with urethane varnish. I checked the level and flatness carefully.
If you use the 2'x4' tile, just be sure it is securely fastened down to maintain flatness.
BO