It is normal to only get one male of a species to show full color, unless you have a large group.
I would get more Baenschi but only expect to have one male. Then you could add one or two species in a 6 footer.
I would choose the Azureus over the Fryeri because Fryeri are more dominant.
Real C. chrysonatus rarely show full male color, though they are often mislabeled, not much for adding color but they (if real) are very unaggressive. Sometimes even Azureus are sold as Chrysonatus, as it is an old trade name.
Lithobates Zimbabwe would work fine as a 3rd group, very different from the first two, are not very dominant.
I wouldn't have any problem with adding juvenile Taiwan Reef, they are very different from you first two fish, and not terribly dominant.