I've done breeding colonies with Petco mice but they are generally inbred to begin with so you are constantly culling. Whenever I got them from a breeder (he got them from labs), I didn't have as many issues with cannibalism. As for food, I always fed mouse chow with supplements of nuts and seeds. Many nuts have higher protein content than the chow does. They were also given unlimited alfalfa/timothy hay. It allowed them to choose what they felt they needed. Some were content with just mouse chow while others ignored it in favor of the other options.