i dont understand it. every village can produce all possible stuff by there own, and its not realy hard to do that. also steel u can produce in large amounts with not that hard work.
idea: why not diffrent regions on the map where diffrent seed grow up. for example: grapes only in south, wheet in middle and so one (maybe some stuff very rare). this type of ressourc differ (and more) could be start a very traffic trade marked.
greetings