I also use a Kobo with Calibre-web and it syncs fine. It’s been about a year so I can’t remember specifics. I remember modifying settings in my Kobo to point to my Calibre-web URL and in Calibre-web settings allow Kobo sync and then make a Kobo shelf. All the books in Kobo shelf are what it syncs too
You just need something that points *.poseidon to your server IP. You can use a host file, local DNS server, or DNSMasq.
Once you have traefik setup, it will have a config where you can setup routers that route the subdomain to a service. Then you have services configured that point to a IP and port.
I based my setup on Techno Tim’s video here and made minor tweaks. Try following that tutorial and see if that gets you started. Feel free to ask any other questions if you run into snags.
Register a domain if you haven’t already. I did two, one for internal and one for external. If you want something easy to setup, use nginx. I’m sure there are guides out there to add Let’s Encrypt SSL certs to nginx. I personally use Let’s Encrypt with Traefik as my reverse proxy. Traefik has a little bit of a learning curve, but once you have it setup and working, it’s pretty easy to update and move around.
Once you have your reverse proxy working with a SSL cert, you can start looking at different options to expose your containers. Probably the easiest method is to point your domain to your home IP address and on your router setup port forwarding. I’m not a fan of that because it’s probably the most risky exposing ports to the wide internet.
Another option is tunneling, which I think is the best. Cloudflare tunnels is pretty popular and I believe are still free. I have a cheap VPS that I have a Wireguard tunnel setup. With either tunnel option you don’t have to make any changes to your home network or firewall.
Do you have conditional forwarding enabled in pihole settings? I think you need that.