desired flow in the tank is based upon what you have in the tank, not its size.
Turnover (water flow thru sump/filtration) is based upon tank size and what you have in the system.
SPS req more flow than Softies, Fish req little at all.
Heavy bio load = increased filtration(turnover helps in this)
Low bio load req not as much
What is in your tank? What do you plan to keep in the future?