I think trying to do this would very likely endup in disaster, first I would really forget about scorps BAD IDEA. Turts and snakes as well, turtles carry patogens that are deadly to snakes and lizards, and snakes can introduce desiase and even hurt your monitor. I also dont know what you guys think but I dont think is a "pretty" thing to do, feeding reps to other reps outside the extreme specialists that dont take anything else, but I will leave etics aside. They wouldnt also breed in a rate that your monitor can take advantage of, at least the turts. I think the best possible outcome of your project is if you filled your pond with a few species of tilapia and let them breed, your monitor would have to take its fishy snaks. As a side note dont feed anything to him that you dont know for shure 100% its safe, this guys are tough but they are not unvulnerable to pathogens or poison, if you trully love your lizard stick to a diet of safe food items. By the way you can also breed easily african land snails wich are a very good food.