I think if he's going to be "rubbish" he probably shouldn't have the blood of a Banespike in him. Especially considering who I *think* the Tzeentch Champion is going to be...
He can be sired by the random vampire in a moment of desperation, then found by Kraskor after the Blood Dragon kills off the fleeing vampire. Then he's taken on as a companion*, and you'll probably accompany Kraskor to Nehklior's Tower in the Land of the Dead whilst he learns magic. Then Kraskor can teach Alastor combat skills at the same time.
* slave