As I suspected. What you have to realize is that your catfish won't care about the extra gallonage, only the extra 12" from what you have now. So you really shouldn't add too many more bottom fish like catfish. I wouldn't add more than 2-4 total to what you already have. As for the red eyes, same applies. You could have gotten more had you gotten the 40 long.
What I would consider is getting some top water fish so that your tank will have action on all 3 levels ( top, middle and bottom. ) Some suggestions for top level fish would be Pearl or Blue or Moonlight Gouramis, Paradise fish, Zebra or pearl or leopard Danios or Golden wonder killies. Stay away from the Dwarf Gourami family ( more commonly found in box pet shops) like Dwarf, powder blue, flame, Honey, sunset gouramis as many carry a virus that is incurable. Some of the other good top level fish either are more fragile or not good for your water parameters so if you ask advice, make sure the person knows your water parameters ( Ph and hardness) before they make suggestions.