Yeah current stocking is already pushing it imo. Discus are very prone to diseases exposing them to wild caught fish is a recipe for disaster. Given that panfish can grow upwards of 6-8 inch and seeing how they hold their own against bass and other predatory North American fish it's gonna end with a blood bath. Additionally as others have mentioned, SA fish need much higher temperatures. I keep my Discus at 86 F. I don't think longterm that will be good for the sunfish. If you like those fish you should set up a native tank but even still you'd prob need a minimum 4 ft tank while 5+ ft would be more ideal from a longterm perspective.
