You probably want to start with a master server like #insight that can launch multiple instances of the game server app on different ports and connect players / spectators to those instances.
#FPS Ranked matchmaking system (dedicated server)
smoky vault
There's a bit of setup to that, and I think it has a basic match maker that you can extend to your needs, but should be better than running long-ish concurrent matches all on one app instance for a FPS.