From previous posters on here, their experiences with Flathead Catfish in small ponds hasn't been great. They are very aggressive and have an enormous gape and eventually will eat out your entire pond. I suppose it could work if you're constantly supplying them with forage... (not sure if they'll eat pellets, but probably not). Looking at your predator list, in just a year, you're going to have over 200 pounds of predator fish in a < 1 acre BoW. Add in all of your other fish, you could be pushing 300-400 pounds of total fish in a year.

Grass Carp can consume 300% of their body weight per day. They can also gain 2 pounds a month. Recommended stocking rates (per acre) are 5-12, with the 10-12 range completely eliminating all plants within 2 years. I might toss in a couple, but until you get a weed problem, I wouldn't go overboard.

"In the age of information, ignorance is a choice." - Donny Miller