the accompanying leaflet states that this is a warm area of China, and
therefore the bonsai is suitable for growing indoors.

Don't believe everything you read in leaflets. It is probably similar to
Serissa & the warmer-growing varieties of Chinese elm. Until we can get a take
on this from a botanist, I would give it a cool rest in the fall & then bring
it indoors, or keep it in an unheated room for the winter, as you are doing.
Try to research a little more about the climate of Gwangdong province, & what
other well known species come from it.

The "Schneidria" is probably something added by the Dutch importer.

Apparently it is a cultivar name. Until we know more, I would put it in single
quotes.

However, this is confusing, as my bonsai guide says that the Zelkova sheds
leaves in Winter, and that has not been the case with the trees which I have.


That is true of standard Zelkova serrata. Have you tried leaving it outdoors in
the fall? It is the short days which cause trees to shed their leaves, if they
are programmed to. This variety may be a nondeciduous type, like Catlin elm.

was advised by the store where I bought the trees that it was ok to use a
houseplant food "pellet" once per month.

Not sure what you mean by pellet. You can use regular houseplant food, but if
it is in your unheated room, it won't need fertilizer more than once or twice
the whole winter.

how much water should I use on the plant each day?

You can't water a bonsai, or any other potted plant, on a time schedule. Water
thoroughly until it runs out the bottom, then don't water again until the soil
starts to get dry. If you're not sure, stick your finger or a wooden skewer
down in the soil.

Iris,
Central NY, Zone 5a, Sunset Zone 40
"The trouble with people is not that they don't know but that they know so much
that ain't so."
Josh Billings (Henry Wheeler Shaw), 1818-1885