Thank you Metro!
However, before I post my strategy, there is one thing to confirm.
I just found out that one rule was changed after the challenge started. From "Learning 16 potions" it was changed to "Create 16 unique potions". It was done when I was already mid-game, and, in fact, I didn't even see it until now... What I did with potions was learning them via experimenting with a cauldron, and after each successful experiment, a copy of the potion was automatically added to my spellcaster's inventory. I ended up with 15 of these (unique), and the 16th one I got when I failed to brew a Potion of Plentiful needs. I didn't grow/find any ingredients and brew these potions manually, except for the Potion of Plentiful needs, which I needed to brew five times for one of the aspirations.
Are my actions different from "creating 16 unique potions"? If they are, I guess it's a DNF for me instead of the win.
Please clarify.