Wow, that sounds like a really nice coop for your chickens! That's a great find, too.
I have a walk-in coop with a lot of windows that open. It makes it so much more pleasant in there. It gives the coop a more light and airy feeling. The extra ventilation keeps it cooler in the summer. In the winter, when the weather is too bad and the chickens are in the coop during the day, it's also nicer for them.
They like looking out the windows, too. The windows are higher up, but they have a platform up high, so they can see outside.
We get more severe winters here than some areas, so we didn't put any windows on the north side of our coop. We usually get a big drift there. Most are on the east and west sides, to pick up the most breezes in the summer. I've also got one on the south side, along with the pop hole door.
We have hinged windows that open completely, so there's a lot of air flow. I'd worry about putting in too many windows if they didn't open, especially if the coop is in an area where it gets hot in the summer. Then it can make the coop hotter than if there weren't any windows. As long as they open, they're great.
We also have hardware cloth over the openings, secured with wood screws and washers. You can also use screws and a board. Just use something stronger than little staples, that can be pushed or pulled out by a strong raccoon. As wood gets older and dries out, it gets even easier to pull out nails and staples.
