The book: Sleepwalkers are potential mages who failed Awakening. Like all Sleepwalkers they do not create Paradox while seeing magic. House ruling: even though they failed seeing their watchtower gave them peripheral mage sight that alerts them mysteries touched by a single arcanum. Example Cynthia Dorn failed to Awaken as a Mastigos but can sense mysteries with Mind Arcanum.
By book: mages suffer -2 To all other rolls while mage sight is active. House Rule: mages can have Mage Eyesight active of one Arcanum per turn with no penalty.
By book: ignore Duel Arcanum rules. House rules from OA will be Followed.