filter would be ok on a 30ish gallon as you are getting a feel for things. If corals is your goal, really ro
water would be much more important so you have a pure start on all water going into the system.
I would look at a 20 long. Several reasons on this. It is a popular size of tank and it wouldn't take the strongest light source to keep some of the hardier starter corals. If you decided you really like going through saltwater, you can easily turn a 20 long into a sump for your equipment that one would have on a larger system like a protein skimmer, ATS, so on. Along with that, the smaller systems are easier to manage issues via large additional water changes on top of the 10% weekly water changes you'd want to do.