This question is too broad/open. There isn't a set number of fish you can add. It all depends on what kind of fish it is. You could always ad a large school of BA tetras, or GD, or even SD.
ok haha, well ill just ask what you would add if you were in the situation, i have a sump with a 700gph pump and a HOB that filters 330gph, the temp stays at a steady 82°
I'd lose the channel cat, get 5-8 more clown loach, and add a school of 6-8 silver dollar. As far as adding another cichlid I'm pretty sure those Red Isletas get pretty big and JD are a medium cichlid so IF I added another cichlid maybe a red severum. Or just do the JD and Red Isletas and bump the schools up to large schools of 10-12 CL and 8-10 SD. That's what I'd do.
I wish i knew how big they got, theres no information about them online at all. also im going to do the schools of loaches and SD's like you said. i like that idea as well, i would like to add one more medium cichlid though if possible
Just get a large school of clown loaches as the only dither, like 8-10... they're one of the most active, colorful and useful freshwater fish you can get... spend all day playing and scavenging for food.
They will eventually grow too big for your tank but you can sell them for a lot of money when they pass 7"... a vendor here sells them for $150 each at 7.5".