Premade coops always exaggerate how many chickens they will hold. The box will say it is for 6 to 8 birds when it will hold just 2 or 3. They want to sell the coops and make them sound as if they will actually work. All those little coops do is make for miserable chickens that get frostbite because there is no ventilation to let the moisture out.
To keep your birds warm in winter think ventilation, not keeping the coop warm. A dry chicken is a warm chicken. You want to vent all that warm but moist air out of the coop. You do this by having about 1 square foot of vent area that is open year round for every chicken up high in the coop. The vents should be above where the birds roost. Making the coop smaller only makes the humidity higher thereby increasing the chance for frostbite. Chickens keep themselves warm. They trap nice warm air under their feathers. You want ventilation but you do not want a breeze blowing on the birds. A breeze will allow the feathers to lose that nice warm air they have trapped next to their bodies.
As for the forum, I have always seen that it is best to have 4 square feet per bird in the coop. It is suggested that you have 10 square feet of run per chicken.
Since you live where the winters are rather chilly you really should think about putting a roof over your run if you haven't planned on doing so. In winter you can cover 3 sides of the run with clear vinyl to keep out the wind. That gives the birds a nice draft free place to be outside during the day. My birds are outside in the run even when it is well below 0.
Think about the birds outside during the winter. They do not appear miserable even when it's cold. They keep that nice warm air next to their bodies. At night they find a place out of the wind to roost.