By the standard formula here, 40.
However, you live where there is a lot of snow. If your chickens will choose to stay in the coop on a fair number of wintry days, then they would be much more likely not to start pecking and killing each other if you used the outdoor formula indoors, which would be 8. It depends on so many things. Is there really an 8x10 usable living space for them, or is part of that floor space taken up by nest boxes and roosts and poop boards and supplies? You have a covered run, but will it be comfortable for them to spend their days in it, not too much wind, not too wet, etc.? The personality of the chickens has a lot to do with it, too.
My coop is a few feet bigger than that and I have 17. I am glad on windy, rainy days that they have the space. It is fine now but I would not want to put 23 more in there. I had 50 in there when they were babies, which was ok, but if we had not gotten most of the roosters into the freezer as soon as they were ready, we would have had problems.
In the end, if they start bloodying each other then you have too many. Each situation is a little different.