Ok what you want to do is level up until chapter 7 where you can get to Shakara. From there is some good enemies (flans and bombs) + kind of a mini boss in the forests named Marduk. When you get your players level 30-40 it might be an good idea to continue into the game to new game plus. After that complete the game and repeat on a higher difficulty. After that you can just play again to Shakara where the best exp and areas are open.