Aha, a fellow Potion Factory enthusiast!
Optimizing for mana generation is definitely the most interesting way to play the game. It takes a few map re-rolls before you get one with the right setup, but you can get some crazy results; I managed to hit one thousand mana per minute on a couple runs:
It should be possible to go a little bit higher if you can generate a map that allows for a Potion Factory adjacent to a Magical Water City next to a Great City of Tech and Magic, which results in a 225% production boost, (applied half again if the Potion Factory is also touching the water).
Makes me wish the game had a map editor so I could experiment!