Nearly any SBC you’d buy would beat the pants off it. If you’re shopping by price then check out a Libre Computer Sweet Potato or Renegade, or a Friendly Elec NanoPi R2S+. They’re <=$40 and should be able to run at least the services you mentioned. If you have more budget, there are $100 mini PCs on Amazon that are great for self hosting tons of stuff, like a Bmax B1 Pro.
Something headless for just running containers? Alpine.
It’s small, boots fast, simple, can run from RAM and Docker is available in its software repository.
An HP Elitedesk mini PC would be small enough to tuck away somewhere and have hardware accelerated transcoding support. Jellyfin recently enabled hardware acceleration for the latest Rockchip boards like the Orange Pi 5 so that’s an option too. If you pre-encode your media into a format compatible with everything you want to stream to then it doesn’t matter, just pick any hardware than can get on your network and run Linux.
I’d try to make it every time but it feels grrrreat
I mean, it works though. I’m not masturbating most of the times I eat corn flakes.
Tons already exist. If you’re in the Pacific Northwest then make your donations to https://www.freegeek.org
Traditional RAID isn’t very flexible and is meant/easiest for fresh disks without data. Since you’ve already got data in place, look into something like SnapRAID.