Wheat....

Just import it. Seriously. No matter how big my farm areas are, they can't keep up with the bread production need. So I decided to just import like up to 1000 of them, and only then my bread production started ramping up without adding any mills or bakeries.

Money? Just tax everything and put tax offices everywhere.

And export berries, fishes, gold bars, jewelleries, herbs, grapes, and wines.