You are right that the weather doesn't get that bad where you are. You should have weather every day or the year where they can be outside, that takes a lot of pressure off of the room you need in the coop. It's not like you are in North Dakota and having to manage in that winter weather.
I don't see any roost space issues. If you have a small handful of chickens you might need a little more roost space per chicken but with as many as you have they will manage quite well with what you have.
People further north than you have open air coops. That's where three walls are generally blocked off with some type of paneling and the fourth wall is wire mesh. Or something like that, some have a lot more wire mesh than that not much further south of you. What you don't want with a cold wind is the wind hitting them where they can't get out of it. That's a wind strong enough to ruffle their feathers when it is truly cold. If you are faced with a cold wind, close the shutters on the wall where the roosts are. That stops through winds.
I think you will need more nests, but you can wait until you see the need before you add them.
Good luck!