For beginner corals you don't need much water movement at all. I've kept xenia, colt corals, brain corals with no water movement but a HOB filter (that just had live rock in it)
if you were gonna do just some zoas, and other softies.. just a couple of cheap power aquaclear type power heads will do it.. you don't need anything fancy. But, if you want minimal space/number of pumps a single gyre is nice.... and on cubes it works very well imo.. (On rectangular tanks, like a 4' tank you get a lot of movement on one side and not much on the other, so you really need 2 gyres if your tank is over 3ft long)