My own Plex server is running on Nuc with Intel Celeron J3455. According to PassMark results, it's very similar in performance to your old Xeon machine. This is why I can talk about the need to add video acceleration.
J3455 included fairly recent build-in Intel GPU which included good support for various video formats processing using its QuickSync feature. On a dedicated video card like Nvidia for example, a sub-system called NVENC will be used for the same thing.
Here's an NVENC Support Matrix:
Find the related video encoding and decoding support for all NVIDIA GPU products.
developer.nvidia.com
One of the more important columns is Max Concurrent sessions. Recently it was at 2 for most cards, recently raised quietly by Nvidia to 3 -
https://www.techpowerup.com/268495/nvidia-silently-increases-geforce-nvenc-concurrent-sessions-limit-to-3
Don't let it stop you as there are patches available, like this one:
This patch removes restriction on maximum number of simultaneous NVENC video encoding sessions imposed by Nvidia to consumer-grade GPUs. - keylase/nvidia-patch
github.com
So Probably cheap GTX1050 like this one:
https://www.ebay.com/itm/EVGA-GeForce-GTX-1050-TI-SC-Gaming-4GB-GDDR5-Graphics-Card/174419724649?epid=20003297363&hash=item289c39c969:g:2bIAAOSwuspY-KqJ
will be probably sufficient.
As I mentioned, a media server client(s) is something you should consider. Jellyfin doesn't have Vizio TV integration and Apple TV only using 3rd party Infuse player. On the other hand, Plex natively supports software for both.
The fine print here is while Plex Pass provides free clients, with Plex Free each client is extra ($5 approx)
But hey, I like free and you have time maybe you could figure out how to effectively used Jellyfin without spending money on supported clients.
Another subject is storage - 2.5TB is very, very little space for video library. Consider that a TV episode is at least 1gig in somewhat decent quality and movie is 4-5gb for a regular 1.5h flick. If you noticed I said my plex is NUC, which clearly doesn't support the space needed, not an issue for me since I use Freenas as storage only and plex server on a separate platform. In your case this hardware you would probably be ok running FreeNAS (aka Truenas Core) on it and plex on another box.
So you have several options: Go all free - Ubuntu and Jellyfin or Unraid with Plex - all decent options, later would much easier to set up and use, but more expensive. It all depends on your tech skills comfort and available time.
You could also mix and match OS and Media server (Ubuntu with Plex and Unraid with Jellyfin
Application Name: Jellyfin Application Site: https://github.com/jellyfin/jellyfin Docker Hub: https://hub.docker.com/r/linuxserver/jellyfin/ Github: https://github.com/linuxserver/docker-jellyfin Please post any questions/issues relating to this docker you have in this thread. If you are not usin...
forums.unraid.net
)
Edit: You could use ZoL or ZFS on Linux to have FreeNAS like ZFS storage system running on Ubuntu Linux.
One of the main ZFS benefits is a self-healing system which cures
bit rot problem - a common problem with many filesystems