start small, and you should be able to do it no problem.
first off, ignore the wd. its storage. you dont want your storage and your processing mixing (i wouldnt anyway)
- find yourself an old, shitty pc with >=4gb of ram, processor irrelevant.
- slap a small ssd in, or dont. install linux
- install docker
- start installin containers
lots of available, preconfigured containers with instruction over at: https://hub.docker.com
when you get your containers functional you can connect your media software (jellfyin) to the wd storage