Congrats to this mission, the first of yours that I tried. Great and strict idea to get all the required goods only on a roundabout way.
The scenario isn't "easy" in the sense of "simple" but requires careful thinking and managing of your people and the resources they bring in. What a shock to notice that there are no hovels available to enlarge the population. (Next to a massive stronghold this seems like a curse.) Bandits and theft from granary provide the appropriate thrill.
Played on very hard at once and would have met the bread request just in time (with only one millboy in action). Unfortunately the granary is disabled, too. And the 300 bread needed for victory didn't fit into a single granary.