Assuming that no floorspace is taken up by feeder/waterer (probably not a valid assumption in that size coop), 4x8 is 32 sq ft, which is 3.2 sq ft per chicken.
*I* sure wouldn't do that for chickens in a nasty-winter area. The chances of getting into picking/cannibalism problems are substantial, and it will be hard to keep good air quality (especially since smaller coops like that are not as easy to ventilate without drafts on the chickens) thus your frostbite risk will be higher.
So, I mean, you can try it if you want. It might work, some people get lucky. On the whole, however, it would sure be better to have at LEAST 2x that size coop (or half the chickens); more space would be better. (Having tried various arrangements, I won't go lower than 10 sq ft per chicken indoors, myself -- similar climate to yours, here -- and really find that 15 sq ft per chicken indoors, plus covered windblocked run, works noticeably better)
Good luck, have fun,
Pat