A dozen will feed you chicken for the YEAR?!? I easily eat 4 or 5 chickens a month MYSELF, plus my wife and son will put away another 2 or 3.
My experience is Cornish Cross don't do well with other chickens because they're still just chicks even though they're almost the same size as the layers...
I hatched out a half dozen Bresse chicks which are 5 months old at this point; I also bought 6 Rhode Island Red chicks from a guy who has a line of heritage birds the same day the Bresse hatched. The Bresse birds are significantly larger than the RIRs, and have been since about week three.