Patrick!!! welcome to Plex. One of the best things to read is this Plex, 4k, transcoding, and you - aka the rules of 4k - a FAQ
It will bring you up to speed on the concepts, like Direct Play, and hopefully some of the limitations of current hardware. The next article has a lot of gory details about the mpv program engine that outputs the video for Plex.
So given that your goal is to direct play HDR from client to TV, you’ll likely need a Shield or an AppleTV 4K in the chain, because they are designed to output HDR to a TV, thereby eliminating the need to fiddle with mpv and Plex Media Player.
A NAS plus an Intel NUC plus ATV4K is a strong option. You’ll want a UPS if you use a NAS.
