Like mentioned above, by the time you get it done the way you want you can purchase one.
If you still want to use this one, it appears as though you already have one window, so you would only need one more. Cutting it would be no problem. Cut the window, then sew(by hand with a needle and thread?) about a 2" piece of material all the way around the window so it overlaps the the tent. Then add several pieces of velcro to the "overlap" to keep the window closed. As far as the camo goes, it might blend in better than a lot of the new patterns...especially for turkeys.
To black out the inside, just spray paint it. If you are going to use it for deer, you might need to let it set for quite a while for the paint smell completely dissapears..if it ever does completely.