".......I am working on long-term plans for self-sufficiency, oriented to
buying some bare land and building an off-grid house, rainwater catchment,
composting toilet, etc, etc ......."

If you put up a couple of poly tunnels, then catch the water from them and
your dwelling into a quarter acre lake you could also keep yourself in
fish.
But really this question is like "How long is a piece of string?"

I would get as much land as you can afford then you can develop as much as
you find you need.
You say on your own, but things could change and you might want to support
more than just yourself, so spare land would be useful.
If you have no other use for it then graze an animal or two for sale to give
useful cash.
Remember for meat it is more sensible to keep things like poultry and
rabbits than larger animals as they are table ready in weeks rather than
months or even years.

--
David Hill
Abacus nurseries
www.abacus-nurseries.co.uk
***2004 catalogue now available***