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).
The OptiPlex draws 15w at idle, about 85w when converting video. My NAS draws about 5w at idle. I initially tried serving media from the NAS, but it’s performance is frankly abysmal. Instead I run Media Monkey, Jellyfin, and another media server on the Dell, which has no problem streaming to my crappy Samsung TV (not using an app, just the crappy built-in DLNA client) It works even better with decent devices, like my phone, laptop, iPad.
Your biggest concern with that Dell is the power consumption. As I said, mine happens to draw 15w at idle - I got lucky
What are the specs on your OptiPlex? Is it a mini tower or SFF? That would help more than just telling us the model.
Depending on your sensitivity to failures (drives die) I’d get 2 data drives for the Dell and mirror them, using the current drive just for the OS.
The local hardware is limited (That’s the export control).
But I believe the consumer-accessible signal from satellites is also limited on accuracy.