Chris make certain about your expenses man. I started my 20 gallon back in March not really knowing how crazy expensive it can get. Listen, all of the people on this site are awesome and really help a ton. But I know how it is especially on a tight personal budget. It IS expensive and does require that you make wise, and sometimes pricey investments. It's all relative of course. To some people, $500 for a good bowfront tank is nothing and live rock at $9 per pound is fine. I would suggest you take some days to "cool" off from the rush of buying the tank. Use the cooling off days to read, read, read about the hobby (the water changes, the chemical balances, the fish feeding, the water quality, etc). It's a GREAT hobby, but requires a good chunk of change and even more dedication. More than anything...patience! If you are genuinely interested and geneuinely have the bank to do it, waiting a few days won't kill you. Wait and see how you feel after 4 or 5 days.
My 20 gallon with the heater, light, hood, powerhead, filter, testing kit, salt (to mix and make saltwater), sand (I bought live sand) and I made the horrid mistake of using a fish to cycle with...all of that cost quite a bit. Then I added a 2nd powerhead, live rock at $9 per pound, and the livestock, you'll need a net, a scrubber, a siphon, buckets, and it's highly recommended you get a quarantine tank (which has to be maintained at the proper water parameters) and 2 extra heaters (for your water changes and the quarantine tank). Think it through, read, and decide.
...No seriously, I don't know what I'm doing.