So you have a bunch of fish that do not grow too much. The biggest problem that folks have with larger aquariums is that they choose fish that grow to the size of their tanks-like some cats, barbs like tinfoils,  and parrots, etc. 

You are fine. You might get some schooling fish like Danios. OR you can just leave it alone. 

My 75 has a few severums, jelly bean parrots and gourami's, but i know that the parrots and sererums Do grow-and Big. So I have only about 20 fish in the tank. 

All depends on what You want for the tank-Show tank for Others-or just yourself. 

You have a lot of room to play with, assuming you are maintaining that tank properly, good filter, staying on top of water changes, not grossly overfeeding...

It would be a dood idead to add a few more buenos aries tetra!

After that you could stop and keep a lightly stocked tank.  

Or you could add more fish.

I would add somthing for the botom level.  somthing like A single dwarf pleco like a bristlenose, or a school or cories, or a school of loaches.  "not huge loaches like clowns or dojos"