The bi-color blenny would hang out on the rocks as the other 3 would swim out front. Depending on the type of goby, it's either gonna hang out at the sand bottom or on the rocks. Have you seen the neon blue goby, or is that what you're looking for in your nano? It's very small and will hang out on or near the rocks.
Bi-colors will not make a dent in your hair algae IMO
. Gotta figure out the source of that. As you add fish and adjust your feeding, gotta watch your nitrates and phosphates. I think those will tell you how your fish load is doing and whether you can add more - along with the inch per gallon rule. Of course, consider that if your fish are small, they'll get larger. As the first 3 are QT
'd and added, watch your water parameters, it'll tell you a lot.
How old is the tank? Substrate? Filtration?