So your coop is probably approx 13'x7' inside.
Do those dimensions include this little add on...or is that separate from the main coop?
Yeah, tight space for 30 chickens and 4 ducks.
Especially the way you have it set up, with odd roosts lengths here and there....and why are those nests up so high? Do all the birds fit on the roosts you have?
Are your bird all young, any cockerels you might be getting rid of before winter?
I would not worry about the gaps in walls so much as the ceiling looks like the roof is leaking?
Adding some ventilation here, by either removing those boards or drilling several large(2" dia) holes would help for when you need to close the windows.
Ok I also have another question, how do you personally attach the tarp? Staples? Tape? Tacks ? And how has it worked for you against the wind
Are you talking about putting a tarp on the run roof?
If so, first make sure that the framing will hold a tarp full of snow...and that there's an angle to shed rain and snow melt.
In this area average is about 20 degrees but the lowest was -37 with about 48 percipatation
Is that -37°F the lowest wind chill you ever had?...and what is "48 precipitation"...inches of snow over the winter or in one storm?