Thanks again, people. To cut bandwidth, a compendium response:-

*** Gordon:

[Hail storms; food storage] Good point. No serious risk of hail
but dust and wind are hazards in deserts. Will crank that into
the setup.

[Goats, sheep, chickens] Useful. Ta. That certainly simplifies
the energy budget considerably, if goats/sheep will eat junk veg.

*** Larry:

[horse stats] Useful figures. Already had horses down as luxury
items; your reasoning provides hard justification. Hence, people
would only endure the cost of owning a horse if it did a job in a
special way. Eg, as a mobile source of power and/or force. Main
use I see is for haulage. I shall downplay the horses: maybe a
couple of dozen in all.

*** Jim:

Also consider Doves as in Dove Cotes, an excellent source of
meat, and also saltpeter for gunpowder

More good points. I already have pigeons as a semi-pest species,
largely controlled by raptors, like kestrels. One food source I
considered was hamsters, which ISTR Andean households routinely
rear in semi-captivity. As rodents (?), they should be able to
thrive on nutritionally dubious scraps.
--
Andrew Stephenson