You don’t have a cold problem at all. Don’t even think about that. Heat is your enemy, but with that down coat they wear year-round, 50 degrees Fahrenheit is just getting comfortable.
Where you are you can see some pretty good thunderstorms and hurricanes are also a risk so I will suggest some shelter from the elements. What I suggest is that at least one wall of your coop be wire. Have one end pretty solid where they sleep and bring the two side walls around to form a bit of an alcove to knock the wind off them when you have that nasty weather. Just a little protection from high winds and driving rain. Put a roof on the coop to keep the rain from coming down on them, but have an overhang. Leave the top of the wall open (cover it with hardware cloth to keep predators out) so they get decent ventilation. You can even leave it open beneath where they sleep. Just have something at roost height to keep the wind and rain off of them.
With 11 hens I suggest 3 nests. That’s what I have right now. They will mostly use one or two, but the third can come in handy. Usually they like to share but occasionally you might have one go broody. Many broodies let other hens lay in the nest with them, but occasionally you get one that doesn’t. I had a hen that was a nest hog. She took about 3 hours to lay an egg and would not let any other hen share her nest. For 11 hens, 3 is a good number.
I suggest you don’t do a wire floor. Instead do an apron around the entire coop and run. Lay a piece of fencing or hardware cloth maybe 18” to 24” around your coop and run horizontal. Overlap it at the corners and attach it to the bottom of your coop and run. You don’t even have to bury it, just lay something on it to hold it down until the grass grows through it to hold it down. Many people remove maybe 2” of sod and put that on top. This holds it down but also gets it out of the way of lawn mowers and weed eaters. The idea is that a predator goes up to the fence and starts to dig. When they hit the wire they don’t know to back up.
How much room they need is a pretty hard number to come up with. There are so many different things that go into it. The personality of your individual chickens and the overall flock dynamics, your climate, how you manage them, flock make-up, and just a lot more. There is a rule of thumb used on here that gives 4 square feet in the coop along with 10 square feet in the run for each chicken. That’s intended to cover flocks from Denver to West Palm Beach, Minneapolis to Phoenix, Perth Australia to Inverness Scotland and with people using all kinds of different management techniques. It’s overkill for a lot of people but it should keep practically everyone out of trouble.
Commercial operations have proven you can keep chickens in about 2 square feet total, but they have to take some pretty severe steps to keep the chickens from eating each other when they are that close, things like trimming the beaks. We generally want to do better than that. They also have chickens that are specifically bred to take confinement well.
It really doesn’t matter if the space is in the coop, coop and run, or they totally free range and sleep in trees. It’s how much total space is available to them when they are awake that counts. You can get by with a pretty small coop as long as they have access to the outside whenever they wake up. You can manage that two different ways. Either have a run that you are confident is predator proof and never lock them up. Or commit that every day of the year they will be let out of the coop as soon as they wake up, even when you want to sleep in on a Saturday or have the flu. Or be sure you can find someone to do that when you are on vacation.
In my opinion, there are three basic things to consider with space. First, the tighter they are squeezed, the more behavioral problems you can have. This can range from feather picking to fighting to cannibalism.
Second is flexibility. If the coop is bigger you might be able to sleep in some on a Saturday. If you find you have one laying in the run instead of the coop, maybe you can leave them locked in the coop until she learns where to lay. If you wake up to a predator problem in the run, maybe you can lock them in the coop for the day and deal with the problem after you get off from work instead of skipping a day of work. If you ever want a hen to raise chicks with the flock or integrate new chickens, that goes a whole lot better if they have extra room.
Last is that I find the tighter I pack them, the harder I have to work. An easy example is poop management. The tighter they are packed the more the poop builds up so it has to be dealt with more often.
I don’t have a magic number for you as far as coop and run space. You probably don’t need as much in January as someone in Minneapolis would. I suggest you give them as much room as you reasonably can instead of trying to really pack them in a small space. I really think you’ll be glad you did.
Good luck with it. It can be fun journey.
