I just started a new colony, but have kept them in the past. I have not had any issues with cannibalism among the colony. My biggest problem was actually feeding the roaches fast enough. Dubia are prolific breeders! I try to keep a 3:1 ratio of males to females. One male will breed with several females, so you don't need as many of them. Having fewer males will reduce fighting among the males since they will all be able to get some. HAHA
Keep the colony warm, humid, dark, and fed, and you will have more Dubia than you can use in no time.