Cories and pleco can go together in same tank, just not YOUR tank. Your tank has a VERY small floor plan compared to a 55 or 75 gal long tank and with already 4 plecos your pushing it if you want to breed. if you added anything else bottom dwelling they will be on top of eachother and cories just keep moving so they will cover the bottom of your tank very quickly and very often disturbing the plecos. I have plecos and mine are always on the bottom underneath something but the corries are always round them, but I have alot more floor space and am not breeding. Breeding tanks are generally for just that... breeding it is not easy and generally doesnt work well to try to breed on a scale large enough with the intentions to sell when done in a community tank. I am no pleco breeding expert but other fish especially bottom dwelers will certainly **** them off being on top of them all the time and if fish arnt happy and healthy they wont breed, thats just a general rule for animals. You may have experience with fish, but your asking about breeding a certain type of fish, which people here do have experience with, I would probably listen.