To get it outside the LAN, you just need to forward the port it uses in your router. Example 8096 for regular http requests.
I would highly recommend getting at least a reverse proxy with an SSL cert.
You can but it will cause security issues. You will need to buy a domain and setup a SSL proxy with https to proxy traffic in. After than I would lock down you firewall rules and make sure that a compromise can't escape the isolated environment.
Also make sure you docker container is hardened against excaping as it will improve security when a security hole is discovered in jellyfin