You said that you had nasty winters, which means that they'll be in out of the weather most of the time for months. They need room to do all their chicken things in shelter -- either a large coop or a smaller coop with a run that has a roof and some protection on the walls (many people put...
Is your run fully covered and weatherproof or will they be confined to the coop much of the time?
I don't know if anyone ever regretted making a coop larger than they thought they needed. :D
The Usual Guidelines
For each adult, standard-sized hen you need:
4 square feet in the coop,
10 square feet in the run,
1 linear foot of roost,
1/4 of a nest box,
And 1 square foot of permanent, 24/7/365 ventilation, preferably located over the birds' heads when they're sitting on the roost...