I’ve used as little as a virtual machine running on my gaming computer to a full blown dedicated server. Really for transcoding as long as it has some cpu cores you can have a good dedicated older machine running plex fine. You don’t need a gpu at all for a handful of streams. I think my max concurrent was 5 ever and I only upgraded for maintainability purposes.
I might just have lower standards here, but most of my content is 1080p at best for movies. Having 2k 4K HDR releases just isn’t viable for most people, now at 1080p it is a bit more palatable. I incorrectly assumed his content composition, so yes my setup isn’t for all scenarios.