I have a server 2012 box with 4TB raid that I use for plex, file server, backup storage. Also has a webserver and couch potato, sonarr, etc. I use Hyper-V to run various VMs for those services. And it has a nice little hot-swap bay on the front for the drives. Just a single quad core cpu and 16GB ram does just fine so far.
I stream plex to the Roku on the TV and to a couple friends' PCs. Right now I only backup the irreplaceable stuff like family photos to "the cloud." I use Mega which gives me 50GB free. Good service.
Best of luck in your build. Happy to help if you have more questions