It actually sounds like it wouldn't work too well for freshwater either. LOL
Go to your local pet store. ***** is fine. Pick up one of their ten gallon tanks. It's cheap, and the lights are bright enough to keep a clownfish or two, but you will need to upgrade to Power Compacts (PCs) if you want coral.
Get a powerhead, (Someone on here... say which one...) and a good Penguin Bio-Wheel (Someone on here... say which one...). Then you can begin livestock.
In the Saltwater Fish world, Live Rock and Live Sand is considered livestock... as well as fish, shrimp, and corals, etc.
The sand and rock are called Live Sand and Live Rock because they are full of microscopic microbes that keep the balance between the Amonnia and Nitrate levels. These are important in your cycle, which I will mention in a moment.
Get a piece of Live Rock or two to decorate your seascape. Then, get enough Live Sand to cover the bottom about an inch and a half. After that, you are ready to cycle.
Be sure to get a good Saltwater test kit. Then simply get a piece of dead Jumbo Shrimp and toss it in your tank. (Well, not literally toss...
)
Your Ammonia and Nitrate levels should Spike over the next couple of days... sometimes a week, or more. Then they should start to go down. When all of your test levels are at Zero except your pH, Calcium and Alkalinity, the cycle is is complete, and you will be ready to add fish.
The only fish that I can think of that would really work for this size tank would be Ocelleris Clownfish or Clown Gobies. Whichever you decide, just be sure to follow the acclimating procedure described here:
https://www.saltwaterfish.com/site_11_03/acclimation.php
That's all for now! If you have any other questions, post away.
If any of the experts on here disagree with anything I said, please say so!