+2 C is above freezing, no issues at all in winter.
So the roosts are on what I'll call the outside wall. You could take the paneling off the entire inside wall under the overhang so rain cannot blow into the coop section. That would be easiest. If you do that I don't think you need an opening on the outside wall but it would not hurt, especially an opening higher than the roosts. I'm not sure how strong a windstorm you might get but that would keep any direct wind off of them. Basically what Alaskan sketched.
If you consider your run secure so you are not worried about predators at night, you don't really have to cover the section where you remove paneling under the overhang with wire. I'd be tempted to, maybe something like 2" x 4" wire or cheap chicken wire, in case you ever want to keep then in the coop section only. But that would be for your convenience, not because it is necessary.
