someone else hopefully can give advice about your concern about GSH being bait stealers. My kids are fishing out my unwanted goldfish and are also catching perch and RES. Maybe my GSH aren't big enough (are 2 years old) but have never caught one on a hook and worm or hook and imitation pellet. I only know I have GSH based on them entering traps or getting caught in a seine. Biggest GSH I caught though was about 5".

If you add perch, at some point you will struggle to control their numbers without lots of catch and release to the pan or a limited number of predators. If you put a few SMB in for example and they don't spawn much, the SMB will control perch and GSH at the same time.