I mean is it too far Ed knows what coming and its grim. Its either get Tayley up to par/where he should have been in at this point in the story or they die to the dragon Ed doesn't really have many options. Also the only one in real danger of death in this plan here is Ed because Tayley doesn't know him personally so he has no problem killing him, as was shown he didn't kill any of the other students because he knows them. Not to mention even Tayley's love interested agreed to be kidnapped so even on that front Ed hasn't really done anything bad outside of lying to him.