Sumps, skimmers etc only really needed for large tanks and coral. smaller tanks 3ft under just the same as tropical but with the added salt and diffrent deco Substrate crushed coral sand or something. Fish are much more expensive and thats the problem for newbies as most people will lose fish if they dont know what they are doing. I would go with tropical at first to learn what u r doing then move onto Marine. What size tank you looking at?