OkBlennies are super cool fish with tons of character and also do work like eating algae and pods and things.
I happen to love clowns and am building a designer clown fest in one of my sumps.
If your going with gulf rock id definitely look at a wrasse its going to come with tons of pods and critters that can quickly take over a 20 gallon in no time if population is left unchecked.
Blennies and clowns won't take any shenanigans from wrasse and should keep in check.