i have a 4 x2x2 display tank and my stand is 4 ft with plywood all around the inside to help with noise i decided a 40G breeder 36x18 would be best for me skimmer on left section return in middle and a small fuge on the right side. i have a large external CL pump 3 power bars 2 MH ballasts and a two little fish phosban reactor one running carbon and the other running phosphate media.

i also agree with stated above go with as big a sump as possible BUT leave some room in your stand to accomadate everything else you need.

i wish i had built my stand 2 ft longer with a cupboard beside the tank for extra storage (test kits food ect)