If you have space and financial support then would be best to setup a 220G, the bigger the better and less change to messing up water chemicals in saltwater world. If you setup a 75G then move to 220G then you pretty much throw away all old equipments and buy all new one for 220G (filter, sump, skimmer, power head circulation...etc.) It's long process so you don't want to redo almost all process when moving up to 220G.