First, get a current book on setting up and maintaining a saltwater tank. When I say "current" I mean a book that isn't more than 8-10 years old. There are a lot of books out there with outdated information that will just give you a headache.
Treat the tank like it is an animal itself. It will need lots of attention. You will have to learn how to care for the tank itself before moving on to the really fun stuff. By then though, the tank will be really fun stuff, or a chore. Then you'll know if you really want to put the time and money into the project. The most idiot-proof advice you can get is BE PATIENT! It takes a few months for a tank to stabilize and become a habitable environment.
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