If your goal is to just have a Catfish pond as a reliable, on demand food source, then I don't think other species are necessarily required if you're going to stay on top of the pelleted feeding. I don't think adding a few RES will hurt if you're worried about parasites/snails, and they don't tend to overpopulate like other species of sunfish. You could always try to get RES of all one sex, if you're worried about them breeding and taking over. Larger CC will definitely feed on baby RES, and you probably wouldn't need but a few RES in a small pond to handle the snail duties.
HSB would be a great addition, for both food and sport, and would also eat any YoY CC or RES that may end up in there. My ultimate goal, similar to yours, is a Blue Cat and HSB pond (someday).
If no spawning structure is present, you shouldn't have any CC reproduction at all.
