I agree with miller.
Are you planning to have corals or fish only?
Live rock or dry base rock?
You may be ok with your setup if you adhere to a strict water change regime.
In the long run a skimmer is a very helpful piece of equipement
1. It remove proteins from the water column. (very, very Important)
2. It oxygenates the water.
3. Your friends who dont have a saltwater tank will think you are really scientific when you explain to them what it does and how it works. LOL