sump for 300 gallon

So I just got a new 300 gallon tank and I am doing the preliminary stages of setup for a reef tank. The biggest tank I had before was 110 gallons so this is much bigger than anything I have done before. I know that I am going to do a refugium and a protein skimmer. What other things do you think are essential to put in the sump system to maintain a healthy reef tank of that size?