Apple will start taking pre-orders for iPhone X this Friday, October 27, 2017. iPhone X will be available on November 3, 2017.
According to firstnameatappledotcom, iPhone X will ship with iOS 11.1 (or later). Apple has also seeded iOS 11.1 GM candidates (15B92 and 15B93), publicly labeled as iOS 11.1 beta 4 and beta 5, to Developers and Public Beta testers.