I'm not sure what the point of him doing anything is though if he intended to take the latter path though. Why not just exit the world and not be bothered?
For the reason you pointed out, he needs Ajokli removed as he wouldn't be able to contend with him anymore than he could defeat 5 dunyain and 100 chorae skinspies by himself. Less so , probably. The whole thing would have been a gambit to remove Ajokli and buy himself time to become strong enough to either defeat him outright or to seal him away permanently. From there, he'd conquer the rest of the Outside somehow and become the God of Gods.
Assailing the Outside isn't something that can be done overnight. Maybe, for those that still want Kellhus to be the good guy, his plan was to eventually 'come back' and save the world.