Wish you luck with your surveys/study.
I suspect that this particular part of it will end with the conclusion, "No".
It is virtually impossible, I think, for anyone to be self-sufficient - and I include people who once lived in subsistence farming parts of the world.
The basic problem is that you would need a fairly large piece of land, several pairs of hands, and a
lot of time to be truly self-sufficient. This is clearly not possible for most people living in urban societies - probably not even in rural areas where people would have to try to scrape a living on poor ("waste") land - thus destroying semi-natural environments, green belts and open land. Looking over the moors and dales of Derbyshire/Yorkshire you can see the remnants of farmland allotments started after enclosure in an attempt to make these areas useful for agriculture. They failed but at the same time destroyed the natural environment.
On can foresee the same thing happening elsewhere in the world where marsh, saline areas, mountains, sub-tropical scrub (&c &c) are suggested as potential farming areas ....
Will be interested to hear your findings/conclusions.
PS: our 'self-sufficiency' extends to growing our own herbs, providing our own garlic for 9 months of the year, salad greens for the summer, brassicas (kale, sprouts &c) for the winter along with a variety of beans/peas whenever we can grow them! A long way from self-sufficiency
but a useful land-use ... also our crops are better than anything you buy grow in the shops!
