When the Divine arrives, she has a favor cap of 6. When you reach that, it goes to 8. Then it goes to 10. They are the neutral/good/best ending respectively.
You need 3 viands/secrets/trophies for 1 favor. So if you do the maths:
- To reach favor 6 you need 18 items
- To reach favor 8 you need 24 items
- To reach favor 10 you need 30 items
However, this only applies if everything goes smooth with her. If you displease her, then you will get negative favour, and will need to regain in - using more items.
It is also important to know that items are used in amounts of 3, so having multiples of 3 is a must. I advice having 12/12/6 if you want the minimun amount for the best ending, or a little more if you want some wiggle room.