OK dumb question here, and I did search to limited success, so please excuse me.

I bought the preorder from steam, I have the head start key, I would like to setup my billing but I don't see any option to do that in my account page. So my question is; will I be receiving another key from Steam in the coming days and at that point will I be able to setup my recurring payments?

Yes, you will get a retail key from Steam next Tuesday when the game launches.