BWAHAHAHA!!! Were you stealing my thoughts? You designed and are building a coop that almost seems identical to mine! (Although mine is half the width at 4 x 8.) I don't have a good picture of it because it's obscured by the run I built around it - you can see that in the "My Coop" link under my avatar... But here's a picture of the front of the coop...
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To answer your question I'd add a cool air inlet on the bottom of the coop somewhere with 1/4" hardware cloth to keep out mice and snakes. Since you don't want drafts you can either add baffles inside or a windbreak outside. Or you could have multiple inlets that can be open/closed from the outside... as winds shift with changes in weather at our place I close the vents on the windward side and open the vents on the leeward vent. In my picture above the inlets are the lower openings with the trim around them. That's actually a storage cabinet below the nestboxes (whose doors can be seen above the vents). The cabinet acts as a baffle system before it empties into the coop.
Your coop is looking great! You can't see all the vents in my pictures, but I am below the usual recommended 1 sq ft per bird. We have a lot of wind and I monitor the coop conditions closely. Even though it's below the recommended amount of ventilation, it has been working perfectly well.
Good work and good luck!