Plex

I just did the plex to jellyfin swap, so ill jump in as well:

Folder structure was no issue between plex and Jellyfin. I did have media scan crashes in jellyfin I didnt have in plex, but it turned out to be my very old music library. I used the FOSS musicbrainz picard to add idv3 tags and rename all files with strange characters in the library and the issue resolved.

Jellyfin has lots of great plugins built-in, with more here. The intro skip is excellent, as is the jellyfin ignore if you want to skip some folders. You can also add an empty file named .ignore to any directory and jellyfin will skip it.

I personally think the apps are excellent. The 1st party kodi app is way better than the 3rd party plexkodiconnect. Faster sync, more feature rich, responsive. The jellyfin android app is also very good. For music, I would recommend Symfonium. Its platform agnostic, but works great with Jellyfin.

For https, look at a reverse proxy like Swag. It will explain how to get your certs issued and automated.

For sharing, the best option is to not expose a port to the internet, but rather to integrate with tailscale. This is an always on vpn network that lets you share servers with remote clients, without opening yourself up to compromise. For a remote jellyfin client, you can install it on a raspi with kodi, or use an apple tv, which has a tailscale app available.