Thank you, everybody, for your prompt and helpful responses. It
looks like my initial (NB wild) guesstimate of 30,000 people must
be cut back to 10,000 tops -- good thing I thought to check. As
round numbers always sound fake (weird, really), let's say 9,403.

The point about favouring legumes and rice is worth knowing; but
I've got to allow my characters to have livestock, as a source of
leather at least. I had already considered having them clearing
more brownfield land for crops, so that's definitely on (maybe an
extra 100 hectares so far). Odd corners (totalling around 50 Ha)
have trees growing fruit and useful stuff. Scrap wood, metal and
such are plentiful. It all (well, most of it) makes sense, given
the situation.

Otherwise, it's a lean time all round, with the added plot point
that land is steadily becoming impoverished and production will
continue to fall -- likely, yes? (And I just realised salination
is a likely menace. Zot... Well, it _is_ fiction; I can mention
it as another impending problem.)

Any further thoughts are very welcome.
--
Andrew Stephenson