Your gaming setup sounds similar to mine, but more sophisticated. I also have an offline win7 gaming PC. Unfortunately many games still require windows, but for some it is possible already to play on Linux. And it is just too much effort for me to keep a windows installation reasonably secure, to prevent games from phoning home. So offline it is. To install games, I put the game installer (in most cases bought from gog) on a USB storage device. This doesn't happen too often, I don't have as much time for gaming as I would like to. Like the sibling comment, I too would be interested in more details about your setup