I am setting up a new Plex server right now because I have outgrown my original one with i7 7700k. I picked up a 12900k motherboard combo from Micro Center this past weekend, but I am not sure how many transcodes it can handle. I did some research, and it is my understanding that the Titan RTX is the best GPU you can get for Plex transcoding that is not a Quadro level card. I found this link that indicates how many transcodes Nvidia GPUs can handle (with modified drivers), but I have not been able to find anything similar for CPUs. To answer your question, there are around 35 people (friends and family) that have access to my Plex server, and it is not uncommon to see 10 people on at once in the evenings. My intention is to be able to handle around 30 simultaneous transcodes (1080p to 720p as this is what I am seeing most common) ideally.