Ideal Hardware for JellyFin

[Efficient_Good_5784]

What would be the ideal or recommended hardware for a heavy use case? I want to:
- Have something low power, that I can leave running all the time.

If you want low power (use less electricity), you usually want hardware that will perform slower and probably not ideal for 10+ 4K streams.
If you plug in an external GPU, that will use power, even when it's not being used.
I would also invest in SSDs over HDDs to save on disk electricity too.

- Stream 4k Video at best possible quality.
- Run 10+ high quality streams at a time.
- Would a powerful GPU be recommended?

If your goal is to stream 10+ 4K videos, you can probably handle this if all the clients direct play instead of ask for a transcoded stream.
I'm not familiar with how much streams certain GPUs can transcode, but if you ever need to transcode 10+ 4K streams, I would imagine that you will need a top-end GPU to handle this.

- Any advantage for JellyFin between Linux, Windows, Mac etc?

Linux will be more stable than Windows (ex: you aren't forced to update the OS every month).
Linux also runs Docker better than Windows.
Can't comment on Mac since I don't use it.

- Use DLNA When possible

DLNA support is slowly dying off. Nothing Jellyfin can do about it.

- Be prepared for JellyFin to Decode/Transcode whenever necessary without stuggling or running into issues.

To avoid getting issues with HWA, make sure to enable the correct settings for your GPU and which codecs it supports. Any that it can't handle will be passed onto the CPU so that it can do the transcoding.

- Remote access my home network with a VPN and stream even while not at home. Is there an advantage to having a VPN vs a Proxy server setup?

The most simplest will probably be Tailscale which is a mesh VPN.
As for VPN vs proxy:

• VPN will encrypt data streams
  
• Proxy will only hide your IP address
  

I am not very familiar with Docker, and right now I am running the direct JellyFin install on Ubuntu 22.04 LTS. Any advantage to either method?

With Docker, you can isolate services from the rest of your system. As in, you can have any service running through Docker and install packages along with it that would normally cause conflicts with the rest of your system because all of it will not interact with the outside system.
You trade a small performance hit to achieve way better portability. As long as a server supports Docker, you can run any Docker images on it.