HI Ben...welcome aboard
Are you doing literally fish only or will you be adding some liverock for decorating purposes?
For a fish only tank the setup is relatively simple. The same equipment that you use in a FW
can be used in a fish only saltwater. You want roughly 1.5 of sand such as aragonite or crushed coral, per gallon. You can't use gravel made for a FW
tank in a SW
aquarium. You can use the same type of box filter for the size tank, such as an Aquaclear 110, but you also might want to add a powerhead of some sort at the opposite end to get a good waterflow...marine fish like a little more water movement to play in.
Again, if you go fish only, standard lighting will do. If you go flourescent, you want a tube that shows off the color of marine fish..don't use a regular freshwater range as the light isn't really bright enough. You can also use a 50/50, (Actinic/10,000K flourescent) if you want some of that "marine blue" color; compact flourescents can also be obtained with that same color scheme.
You want to make sure the tank has a good cover...glass or otherwise..some marine fish are jumpers.
Now, in addition to the above, if you are adding liverock, the idea is the same with a few minor modifications. You would definitely want at least a 50/50 bulb. When placing the liverock you want it securely seated in the sand or preferably sitting on the bare glass and adding the sand around it. Remember you are looking at rocks in a glass tank. You want to avoid shifts, either due to unsecure rock or busy fish, where you might get a "landslide." Some marine fish are great burrowers and can shift your entire aquascape. If there are rocks on top that aren't stable, they will tumble.
Just as with FW
, you want to cycle your tank prior to adding fish etc. If you add liverock, there is bacteria in there that can help with the cycle, or, take a piece of raw shrimp, like you would get a grocery store, put it in t a mesh bag (to keep form losing it in the tank) and hang it in the tank. As it decays, it will provide the ammonia to get the cycle started. The cycling with only liverock takes longer, about 4-6 weeks, but adding the shrimp tends to shorten the cycling time to about 3-4 weeks.
A basic list but some may add to it:
Hydrometer or Refractometer (for testing salinity with refractometer being more accurate).
Filter w/associated media (this is a whole different conversation as to the types of filtration but at a basic level you want carbon, the filter sponge and filter floss if you are using something like the Aquaclear Filter(s)).
Powerhead for additional waterflow
Saltwater Test Kit: most of us use the API Master Saltwater (good for fish only) and/or Master Reef testing system (reef system). Avoid testing strips as they are not accurate.
Marine Fish style light bulb
Aragonite or crushed coral at about 1.5 pounds per gallon (may be slightly less with liverock but it can still be used)
As an aside, the FW
decorations such as lava rock and driftwood cannot be used in a SW
system. Any decorations not "natural" for SW
systems need to be either plastic or glass. I know there are coral like molded thinks you can pick up and marine looking plastic plants but these are properly sealed for use in either a salt or FW