This is what I wonder: if you take away all of the advantages of the fossil fuel society since the Industrial Revolution - you end up in a world that would probably resemble the Amish communities quite well. I believe that the Amish are practically self-sustainable - I still have not confirmed whether they truly are, but let's assume just that.

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By taking the modern world as starting point at the premise of being unsustainable, you'll have to take stuff away to get to your sustainable society - eg, you model backward. I would like to know what stuff of the modern world can be slotted into a working sustainable model - modelling forward. That's "working from scratch".

Except that the "modern world" has a knowledge base and a technological infrastructure which allows you to do things that would be impossible from the Amish starting point. But I get your point: assume you start from just an undeveloped plot of land [but in contact with the modern knowledge and technological base] and see where you can get.

I just found this:

The Japanese experience of complete self-reliance in the Edo period demonstrated the sustainability of more than 0.3 hectares per capita given for agriculture, even though the country was not very rich. With less than 0.1 hectare per capita it would be very difficult to maintain even the minimal nutrition level. Note that the world average has decreased from 0.25 hectares per capita in the 1950s to 0.15 hectares per capita in the 1990s, which may be critical for a sustainable level in the future.

Does that mean that you can get away with 1/3 of a hectare per person? I seemed to remember something like 2.5ha were necessary to sustain one person. The world's population density is indeed equivalent to 2.3ha per person. The EU's population density corresponds to .87ha per person (wiki).

Anyway, Barbara and I have this concept we call ETopia, which is basically the 150 most active ETers and their immediate families on enough land to support everyone. If you have 500 hectares of land, €5M of capital and 150 ETers of human capital, can you build a sustainable community for 600 people somewhere in Europe?

Those whom the Gods wish to destroy They first make mad. -- Euripides