If you want to build it yourself, you have to decide on size.
Are you trying to keep it as small as possible?
Do you want a dedicated GPU for multiple jellyfin streams? (Definitely get the Intel A380, cheap and an encoding beast)
If you don’t want to start a rack and don’t want to go with a prebuilt NUC, there are 2 PC cases I would recommend.
Node 304 and Node 804.
Node 304 is mini-ITX (1 PCIe slot, 1 M.2 slot for boot OS, 4 HDDs, SFX-L PSU, and great cooling)
Node 804 is micro-ATX (2 PCIe slots, 2 M.2 slots, 8-10 HDDs, ATX PSU, and 2 chambers for the HDDs to stay cool)
Why do you want a N100? Is electricity very expensive where you are that idle power is a big factor? Because desktop CPUs are more powerful and the CPUs can idle down to 10W or so without a GPU and they can have way more RAM.
Tldr; go with prebuilt NUC or go with a desktop CPU for a custom build.