Did you state which 3 fish you would like to keep in there? I forget....

There's one thing to consider about fish selection for such a small tank. You
should find out where the fish you want to get like to hang out. For instance,
I have a Hi Fin Red Banded Goby (with Randall's pistol shrimp) and a Purple
Firefish. The Hi Fin likes to hang out near the sand and its burrow the shrimp
made for him. The Firefish likes the water column. They dont even share each
other's space so there's no territory to fight about (both fishes are pretty
passive anyways, I'm just giving an example). If I was going to add one more
fish, which then I'd be going into Im-going-to-get-flamed-on-the-internet
territory lol, it would be a Black Clown Goby. They mostly perch in corals
which would be the only place my other fish dont go. Oh, I have a ~12 gallon
tank with a ~8 gallon sump.
~John