Seems like it depends on what you want to do.
Do you want FO (Fish Only)
FOWLR (Fish Only With Live Rock)
Full on reef tank
etc...
There's a ton of different ways to go. Seems like FOWLR is the easiest as you don't have to change so much water all the time because the live stuff in the rock processes the Nitrates, but live rock is pretty darn expensive. FO would be just like a fresh water system, and you'd have to do a TON of water changes (pain in the butt with salt water).
Water changes, you need to use RO (reverse osmosis) water. You can either get a RO unit and make your own water, or buy it from some stores. Keep it in a big tub, trash can, etc... with the correct ammount of salt and pump it into your tank when you're ready.
Personally, I looked into it, and salt water seems like a pain mainly because of the difficulty of water changes. So I decided against it.