whats the space for each pen?
WRT roosters it really depends on the breed. I have always had between three and five at one time. Like someone said the hens tend to scatter about. I have watched my roos post them selves on opposite corners or near the most hens. And Yes the hens will alert as well.
Always an alpha roo in the group... He was the Boss or alpha and squabbles would occure but well within the range of normal behavior. Usually with only a pulled feather or two following a screaming and running session