I think everyone has the list down pat for you...all I can say is do NOT just use chicken wire. It's designed to keep chickens in...not predators out.
My chickens free range during the day, and their coop has a 40x 12 ft. run built out of 2x4 welded wire fencing along with netting across the top (this is for when we go out of town). I lock their coop up in the summer at night, however, during this cold weather, I have a kids swimming pool with a de-icer in it out in the run and leave the back pop hatch open half way for them to go out and get water. I also set a trap every night...this may be something to consider. With the 2x4 welded wire, I can tell you that a cat has to literally ring its' neck to get in or out of that. However, snakes can def. get in there.
I suggest using poultry nails (little u shaped nails) rather than a staple gun for any fencing you decide to use either on the windows, ventilation, or whatever. It is much stronger. Hope that helps.