I did this exact thing with my server. Fully encrypted with a boot partition on a USB.
Clonezilla from my encrypted SSD to another (you can also decrypt it with clonezilla before the copy if you want)
Expanded the LVM volumes
Viola, 120GB to 500GB. Spun up the docker containers and everything just worked again
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.