I remember asking the same questions you are asking. A lot of people have already set up a saltwater tank before they know what they're really doing. It can be a bit unnerving, but with time, patience, and research you'll be just fine!
Jason has already given you lots of great information. Follow his advice, and you won't go wrong. I'd just like to add one comment about corals/lighting...
Before you spend too much time trying to figure out what to do with your Eclipse hood, try spending some time on the web looking at all of the different types of corals - polyps, softies, LPS, SPS - get a good feel for the shapes, colors, and textures that appeal to you. Once you know what corals you can't live without , you can then begin to plan your ideal lighting set-up with your specific corals' needs in mind.