Auloncara will do wonderfully in that aquarium. Don't mix strains, however, as it may become a hybrid factory! Just pick your favorite Peacock and acquire a good number of them. 10 wouldn't be a bad number to start with. IME, 'german red' peacocks are avoidable, and prefer truer strains of peacocks, which will ensure nice color. IME, german reds and other linebred fish are hit or miss in the quality of alpha males coloration.
Syno Multis would be the better catfish for them, IMO, as you have a good chance of successfully mating the synos as well. An ancistrus or 2 as well.
You could also include a pod of labidochromus sp. and possibly a Hap of some sort. The labidochromis complex has numerous local varients and are dietarily compatible with copas, aulons and haps.
Scienochromis Fryeri, the "Electric Blue Hap" would be nice. If you go with the blue hap, avoid predominantly blue peacocks or blue copadichromis, since the the Blue Haps attention may prevent the smaller fish from either coloring up or breeding.
Copadichromis and Auloncara, I believe may cross breed as well, so only use one of these species.
You have lots of choices! Have fun!
