Notes about the system itself.
To expose the files to the internet — partly due to privacy concerns, but mainly because my ISP puts me behind a CG-NAT — the system uses an additional machine outside of my ISP, on a separate auth domain: a tiny, internet-facing Hetzner Cloud VPS rented for around €4 per month. This setup allows me to expose the files to the internet no matter where my file server is located or how badly my ISP treats me. Keep in mind that Hetzner is known for bullshit takedowns, so in the future I will probably migrate to a different hosting provider.
The server, currently available at 167.235.19.20 and 2a01:4f8:1c1c:bcf::1, listens on the /net imported from the remote VPS (which is a little slow, but good enough) on the following TCP ports: