As you may know I have a 28 cal tank with a 25 gal refugium/sump, prizim pro skimmer, 3-4in bed is tank and 6in in refugium, and a pump that pumps 600gph. I curently have a matted pair of black puculas.
i agree. do not over do it on fish in small tanks... alot of people do but they also have some beefy skimmers... The prizm IME isn't a high performer... but if it works for you, Great...
you need to balance... if you are gonna stock corals like crazy go easy on the fish... and vice versa... remember to keep up on your water changes as you have a small system...
Black perc's are beautiful. That's an excellent choice for your small tank.
You need to decide how religious you'll be on the water changes before adding more fish. You tank is small, so WC's will be easy enough. If your willing to do the regularly, then go ahead and add another small fish or two. If you want to be a little more on the lazy side, then stick with the two beautiful fish that you already have.