I've been playing Banished with the Colonial Charter mod and the Adam & Eve starting condition (You start with a husband & wife and some supplies and that's it)
I now have a town of 1200 that is currently able to sustain all its needs without having to import anything. This is the main settlement cluster:
If you look at the mini-map you can see the large food making area just to the left. There are lots of farms, pastures, orchards, fields, mills, bakeries, meat processing places, etc. Along with some hunters & gatherers in the forests I am currently producing 170k units of food while my city only needs 140k every year. The food is distributed around in a network of storage barns and markets. In the following picture you can see some of the pastures on the right and the wheat fields, mills, and bakeries across the river on the left
My city is not sustainable long term. The problem is that I have not been building many new homes. Building new homes drives population growth, which I am trying to avoid. However, the problem with not building homes is that eventually they all fill up, and new families are unable to find places to live until everybody else in another house dies. This reportedly leads to mass stravation events, as people end up being born in large groups all at the same time. The usual solution to this is to build a couple homes every winter, so you have a steady stream of people dying at different times. But the size of the map is limited, and so you can only make so much food and chop down so much firewood
Check out the population graph for the history of my town
You can see where I sort of stopped building new homes every winter. The population growth was just too crazy and I had to cut that out. The graph is starting to plateau, but as you can see the number of students and children is not increasing at the same rate as the number of adults at all.
This is not a sign of sustainable growth at all, and I will have problems when a whole crapload of old people start dying on me and I don't have teenagers there to replace all of them. I am not really sure what's going to happen actually, but I don't like the look of that graph.
It is possible to build a chain of trading posts along the main river, literally one beside the other. Using this method you can "summon" a trader at a regular basis and set up an autotrade to buy firewood from him, selling some sort of processed good that your town is able to produce. This way you don't have to worry about preserving the forests and you can use a lot more of the map for food making purposes. The problem is that it seems gimmicky, but I will probably have to build a bunch of trading posts anyway.
I am considering letting my town run overnight to see what happens to it...