When my family started keeping chickens, we only had 3-4 at a time, because we were experimenting. We then built a large chicken coop and kept 20 chickens and 5 ducks inside. Since it seems like you want to keep the birds confined for the most part, I'd recommend getting a rooster and four hens. Also, what kinds of chickens are you looking into? Larger breeds need more space than smaller ones, so...
Depending on what kind of chickens you get, they may jump the fence. If you want to keep them contained, you'll need to cover the "free ranging" area.
I'm starting out with one medium sized garden shed as the coop but am going to be putting up another soon. And I am free ranging mine. So no fence other than places I want to keep them" out" of we have 6 acres for them to roam on so idk about a fenced in area... I know the coop needs to be big enough for them all to roost and lay and each have enough box room.