If you have a good return pump, you can minimize the number of powerheads. 16x-20x the volume of your tank is the flow required for reef tanks. So, if your tank is a 50 gallon, you need a minimum waterflow of 16x50= 800 gal/hour.
Corals don't like a linear waterflow, it needs to be random. I noticed that SPS will grow weird if the water constantly hits them in one direction. Jolt suggested having 2 powerheads placed in each corner and pointed towards the front middle part of the tank. This is an inexpensive alternative to a wave maker.