I wish I'd found this thread a while ago. I just built a system really similar to yours, down to mounting the ballasts on painted concrete block wall!
My system is 8 18 gal tubs, 2" pipe to 3/4" return from pump. I put a T in the return to the rez so it would have two waterfalls. Big pump driving 4' flexible air stone each tub. rez is 35 gal. 2 1K hps but I'm only on day ten of clones so, got a while before 12/12.
EDIT: I only got to page 6 before posting but I see that you changed your system... my system is undercurrent. what's your new system? why'd you change?