The sub model used is the auto renew. You can stop the sub through iTunes. Since we will not be pruning accounts if you wanted to stop for a while because you'll be away you can resume your sub at a later date and whatever your status was when you stopped will be retained.
We are in your boat, we figure people are either going to love the game, or hate it.. Pretty much any strategy game is that way. We'll also encounter the "No single player, no play" as well. I did make a comment in a dev meeting once that I could let the player choose at the start if they want a single player experience, if they enable that I'd disable the e-mail, and chat systems so everyone seems like an alien.