Used PC for media server

[TheDreadPirate]

6th gen Intel CPUs do not support 10-bit HEVC decoding, which is required for tone mapping. All of the HP systems you listed have 6th gen CPUs. The additional RAM does not benefit Jellyfin. In my experience, 2-3GB is the most RAM that Jellyfin uses for my 8 users. Usually 3-5 simultaneously. For your user count, 8GB is probably plenty.

Since the 3070 does have a SSD, the extra $30 is may be worth it for 2 more cores. Having said that, I haven't felt that the 4 cores in my 12100 has been a limitation. I'd choose whichever has the bigger case to accommodate a dedicated GPU down the line.