Just use the OptiPlex for everything. The RPi lacks the horsepower, and storage capability.

I’m currently using a 7 year old OptiPlex SFF as a NAS, backup point, media converter, and media server. I’ve upgraded the storage drive to 8TB.

I do have another old NAS I use only to duplicate my data store locally (I keep 3 local copies of data, and a cloud backup).