I also used recycled windows. However, now I wish I had not. One reason is, it still has to be covered with hardware cloth anyway, to keep the coons out.
I have seen, here on BYC, what I like better is .... simply, openings between the studs covered with hardware cloth. No measuring to do, no studs to cut, and it doesn't matter what size! Just a hole with hardware cloth!
Then, just fashion some type of "window covering," to be used in harsh weather. This can be as simple or elaborate as you want. I like the ones that are a piece of plexiglass and slides over the opening. I also like the ones that are like a picture frame, and can be hung on hinges, to open horizontally or vertically.
I'm sure not much help, on how to hang a window, am I !