Hey, good questions.. alot of people dont realize the importance of water movement. In my 72, Im using two maxijet 1200s (295 gph each), one extra maxijet 1200 feeding my Remora Pro skimmer, and two Magnum 350 canister filters (350 gph each).
Recommended flow depends on your type of setup (fowlr or reef). Reef always demands more flow (10x-20x), although its important in a fowlr too. You want to shoot for at least 10x turnover per hour in your tank (through filters and powerheads). And yes, my powerheads run 24/7.. and I use foam prefilters to discourage livestock from getting sucked up.