Do yourself a favor and pick up or borrow a copy of The Conscientious Marine Aquarist by Robert Fenner. It has all the information you need to keep a saltwater aquarium
Basically, your filtration consists of aragonite sand and 1-2 pounds of live rock per gallon, and I would also invest in a good protein skimmer.
You will want approximately 3-5 Watts per gallon of heater, I would split that between two smaller heaters instead of one large one, heaters are the most failure prone gear in this hobby.
You'll also want powerheads to move water in your tank, you're looking for 20x-40x tank turnover rate. Look at Maxi Jets, Koralias, or EcoTech Marine Vortechs (the Vortechs will give you random flow - but they are pricey)
The most important decision you need to make is if you will be keeping fish only, or if you want a reef tank. If you plan on a reef, you will need to look into lighting, and it will be the single most expensive purchase for your setup. You can look at T5 HO, Metal Halide, or LED's. As you do research feel free to post here with questions. There are a lot of Chinese knockoff fixtures out there, most of them will end up costing you more in the long run that buying a quality fixture