You can go further (I added some screenshots here) but where I'm at, I can only advance in terms of levels and max stage reached on each area. I don't have any more objectives to look up to.
You can make yourself more powerful by:
- increasing the level of course
- upgrading all equipment (you can unlock all 10 pieces)
- upgrading the pet
- and, notably, just killing thousands and thousands of monsters as you will see in the Bestiary that each milestones gives you more stats
I assume it's possible to reach all the way to 50 in each area if you keep on grinding.