i just followed the sphere grid and started maxing my stats after gaining control of the airship to avoid being mixed up..

Cactuar king and Don tonberry are great in AP hunting, but its not just AP that you need, you also need GIL... so the best way is to equip triple AP weapons in the omega dungeon when you are strong enough, you get AP and cash by fighting mimics(50,000G |100,000G if equiped with gillionaire ability)..for me it really wasnt hard, i even maxed out my luck(not really needed).... not hard, but very very boring