I think some of the most hardy types of saltwater fish include; clownfis, a few different variety of gobies, green chromis, cardinelfish, and others. If you want some that have that predatory aspect, those tend to be slightly more hard to maintain in a new tank due to their requirements (and how they are limited in their stocking options compared to ones that are good for starters, like you).
Maybe once you have a good amount of time understanding saltwater, handling some of the hardy fish, and others, it might be wise to then start researching some of those other aggressive options for your aquarium tank that fit within the fish you have in there already.
