Sucks having made an initial investment but at least you're aware of the limitations of your set up and your birds will definitely appreciate a new coop in the spring. I did the same, making smaller investment initially with just a few birds and a prefab, then upgrading later on once I decided...
You want to keep as much ventilation open as possible however I'm not sure where the ventilation is in relation to the roosts, and how the wind/breezes interact with those vents. So that's something you need to look at. If push comes to shove you can see if there's a way to add a buffer by...