With that few chickens, it might be difficult keeping them going through a Minnesota winter. They will most likely require supplemental heat.
We have 40 chickens in an unheated coop that is by no means draft-free. We actually left the two south-facing windows uncovered this winter to increase ventilation. The chickens did much better this winter than in previous ones--with all the windows shut up the ammonia build-up was quite bad.
I live in Nebraska, garden zone 5a, and our winters can be fairly severe, though not so severe as yours! We purchased but have not installed a 400 watt eco-heater, which is simply a ceramic radiant panel. It's currently being used in the human house!
The shed might be able to be converted into a chicken house. What is it made from? Are there windows? Are you planning on enclosing a chicken yard, or is there a fence to keep them safe from dogs?