I agree that it is better to not feed fish live food, but if the feeders are healthy there is nothing wrong with it. Personally, i would feed my fish feeders, but not gold fish as they arent very nutritous. I'd feed them bull head minnows, guppies, convict cichlids. I have fed my fish convicts as feeders, but it usually consists of various frozen foods.
Very nice fish though, and im glad your getting a bigger tank. I have been interested in nandus nandus for a while, how big of a tank do they need and how big do they get? How big are your nandus nandus now?