Lastly, if you're looking at the COTA list, check out the salvini he has. Both strains are among the reddest you'll find. These would be perfect for a small group of two pairs and a coupe extra female is the tank you're planning. Much better than a single pair of larger heroine cichlids where males can go beserk leaving you with a lone female (I'm talking about the grammodes).
You can try to source some astyanax tetras as dithers/target fish. Salvini will rip up livebearers. They are found with quiet a few other fish. Heck, one of your spare bifas would make a nice centerpiece and you'll have a ton of color. If not a bifas, you have plenty of others to choose from in the usamacinta drainage.