Not sure what your management style is, but if you keep them confined, or confined over the winter, make sure you have at least 14 sq feet per chicken (minimum of 4 sq feet in the coop, and 10 in the run, with access between the two whenever they're awake). If you have to keep them confined at all during winter, or for weather events, make sure they have a covered run/coop and at least 14 sq ft per bird. It does depend on the temperament of the birds somewhat, but if you go below that spacing, they can have some pretty significant negative behaviors that start due to crowding, boredom, and stress. Some breeds need even more room than that, and some can make do with less.
Ask me how I know.
I was one of those folks who wanted 4 chickens and ended up with 19 also, my first year with chickens. We're now down to 14, which is still probably 1-2 chickens too many for my 200 sq ft covered run/open-air coop. But the 14 seem much calmer already. I have Prairie Bluebells and Starlight green eggers (both flighty active leghorn mixes) and ISA browns (red sex-link RIR mixes). The PBBs and SGEs can get pretty anxious, and the ISA browns are pretty mean to other chickens. They'd probably be happier as separate flocks, but that's a project for another day...
