Chickens like to lay eggs in groups, so if you had 1 nest per chicken, many of the nesting boxes would be empty, and several would have many eggs in them. I have 20 hens and 5 nesting boxes, and on a typical day, 3 nesting boxes have 4-6 eggs in them, and 2 nesting boxes are empty. And the empty ones change from day to day. I even have hens waiting for another chicken to come out of a nesting box so they can lay, even then there is an empty nesting box next to it! Their have a natural desire to have a clutch of 8-10 eggs so they can lay on them, and they don't care if the eggs are their own or a communal nest.
I would definately let them outside in the winter. Some chickens like the snow, others do not. I put a roof over my protected run as I got tired of shoveling the deep snow out each storm! Now I cover the wire walls with heavy duty clear shower curtains, and this keep the wind and snow out. The chickens and ducks are very happy with this arrangement. Of course, the ducks would like it if I could keep the kiddie pool filled with water instead of ice, but that's another story!