Well, he hears the Voice of Satan, so...
Strangely, despite his massive realm and the huge number of bad traits, there was only ever one small revolt in his reign. The first ten years involved some very, very careful moves to bribe/flatter/murder/imprison troublemakers. The next ten I spent less time worrying. By the end, I just stopped managing the realm entirely. My vassals all loved their crazy God-Emperor.
Test them. Marry your mother. Convert to Hellenic paganism. Declare war on the Pope, the Byzantines, Venetians, and everyone else. Randomly pick five vassals and imprson and banish them. Then kill your mother.