Best thing to do- hold off on setting the tank up until you have had time to do a little more research/planning. Search through the threads on this site, & check out some related books. A good one that is easy to understand is "The Conscientious Marine Aquarist" by Robert Fenner.
Next, in order to decide what equipment is best for you, you'll need to plan out what you'd like to keep in the tank. Fish only is a lot simpler, but then if you ever plan on adding any corals or inverts later, you may end up wasting a lot of money on all new equipment.
If you're going fish only, the wet/dry & canister would probably work, & you wouldn't really need too powerful of lights (regular fluorescents would suffice).
If you want to ever keep corals or invertibrates, you'll need more powerful lighting & a protein skimmer. VHO or power compact fluorescents are OK for some corals & inverts, but many require even more powerful metal halide lighting. When you decide what you want to keep, you can better narrow down which lighting is best for you.
A sump, while not a necessity, is good for many reasons- first, you can place equipment, like a protein skimmer there so you don't have to put it in your main tank. Next, the sump increases your tank's water volume, which makes it more forgiving regarding chemical changes. Also, you can put "problem" critters in the sump so that they won't harm the main tanks inhabitants. Search this site for "Sump" to read more about sumps & to find do-it-yourself plans. Or, like maxx said, you may be able to modify your wet/dry into a sump- if you can post pictures of it we could possibly give you some pointers on that.
Live rock is not necessary for a fish only tank, but is decorative & helps increase biological filtration. Definitely read more about the Nitrogen Cycle & biological filtration before starting. Also, you'll want to invest in a good test kit (Salivert is a good one). You'll AT LEAST need to test for Ammonia, pH, alkalinity, phosphates, & nitrates/nitrite. If you add inverts or corals, you'll want to test for calcium, too. If you get into adding supplements, you'll have to test for other things like iodine, strontium, etc, but that's only if you add these supplements, which, in my opinion, really aren't necessary. Once you are familiar with the nitrogen cycle, you can start cycling your tank (use a frozen shrimp like Gina said & skip the Damsels). When your tests come out to acceptable levels, it is then safe to start adding critters.
When adding critters, make sure you know which ones are compatible with eachother, & if you want to keep corals, which ones are reef-safe. A lot of critters will eat your corals!
Finally, the issue of whether to have a deep sand bed, crushed coral, or bare bottom is kind of controversial. Each has it's benefits & drawbacks. You can read more about it in this thread:
Put the gloves on and let's talk DSB.
There are also a lot of helpful sandbed-related links on this thread:
Sandbeds and how to use them
Hope this helps get you started. The most important thing is to be educated about what you are doing. You can minimize major problems by thoroughly planning and researching each step of your tank's set-up. Once you have more specifics on what you plan to have in your tank, etc, we can give you some more specific pointers. Welcome to Reef Sanctuary!
