In the classifieds, you probably won't get anyone answering this. I'm going to move it to New Hobbyists, and folks will help you out.
To start, this is VERY DIFFERENT from freshwater, much more expensive, less forgiving, and very different in terms of stocking a tank (far fewer fish). I would do a lot of research and thinking about the animals you would like to keep, draw up a budget of what you can afford, and get the largest system you can. Small tanks are more difficult to keep than larger in this hobby :yes: