I would suggest you connect that coop to a covered run, and put up wind blocks for winter.
True inside floor dimensions would give us a better idea of how many chickens would be happy.
But, a roofed run with good wind blocks, is almost as good as a coop. Truly. Also, with a roofed run with wind blocks, you could then stick a huge vent on the side of the coop that is now protected by the run roof. Then you have ventilation in the coop protected from rain and snow.
True inside floor dimensions would give us a better idea of how many chickens would be happy.
But, a roofed run with good wind blocks, is almost as good as a coop. Truly. Also, with a roofed run with wind blocks, you could then stick a huge vent on the side of the coop that is now protected by the run roof. Then you have ventilation in the coop protected from rain and snow.