I'm by no means an expert but:
- Yes it is, that's what https is for (your reverse proxy in that case, best to host Jellyfin and Nginx on the same machine to prevent any unencrypted traffic leaving your machine)
- They won't, unless someone accesses your Jellyfin via http
- Yes they will
- Yes
You could use a Cloudflare tunnel to hide your IP from your users, but that will give Cloudflare the ability to decrypt your users traffic. They shouldn't do that though, just wanted to let you know they could
Hiding your IP shouldn't be necessary though imo, unless you really need to (Cloudflare most likely won't help with that)
Also make sure to setup a Firewall if you plan on exposing your server to the internet!