How much LR and is it a reef or FOWLR?
Koralias are a great powerhead but limited in controll and versitality which to a newbie can be very usefull. I would get 1 #4 and a powerhead with flow control knob and duckbill tip for dirrection control.These also are very usefull for water changes as a plastic hose will let you drain and fill for changes.
Then depending on amount of rock , placement , coral and amount of stock , you may beed another powerhead for spot flow or better flow.
Here are a few good articales.GL.
http://www.drsfostersmith.com/pic/ar...id=285&aid=243
http://www.advancedaquarist.com/2007/1/aafeature/view