If you do not have a lot of records in the database tryton will not have a loot of memory usage. IIRC I think you can run PostgreSQL and the Tryton server with 512MB of RAM. Not sure about the disc requirements but the docker image with libreoffice installed only requires ~300MB
Yes you can run on a pi computer. AFAIK the gnuhealht project are deliverying raspberry computers with GNUHealht installed. So it’s possible to do the same with only Tryton.
Yes, this is also possible altought probably using linux will be more stable and secure
IIRC there was a guide on this forum to install the tryton server and postgresql on windows.