A BGK would do best to be fed a varied diet of bloodworm, brine shrimp, blackworms, chopped earthworms, mussels, prawns, the occasional mealworm; and occasional veggies such as zuchinni, squash, potato etc. Many of these foods can be found frozen and live. BGK may also tend to scavenge and clean up leftover flake and pellets at feeding time!
I am not sure about keeping it with chiclids/angels, you certainly don't want to house this charming fish with others that can be aggressive, they are sensitive to meds and poor water quality as well.
BGK will also exceed 18 inches in length, somewhere down the line it would be in the best interest of the fish to obtain a 75 gallon tank or larger.