I actually currently have a colony of 15 f1 kigs at a small-with a few getting close to med. size. They are a mix of 2 seperate batches but the same parents and they do fine together. They are generally verry skiddish and will scatter when the lights come one its normal. I feed my fronts NLS sinking pellets as long as they sink you are good. I actually keep a Neolamprologus helianthus with mine and they seem to get along fine for now. Once the fronts get a bit more size on them the helianthus has another tank with some tank mates to go to. You are correct that they grow slow and will need a larger tank. Depending on how large of a tank you plan to get will tell you how many you can keep, a 125gal should be good enough for what you have now plus 2 more. I will say the sooner you invest in a larger tank the better off you will be and you can easily get more. If you plan on breeding them make sure you trade out your males for males from different parents.