Internal 5TB 2.5" drives are expensive for their capacity and don't fit in many consumer 2.5" bays due to their excess height. You're better off getting a 3.5" external that you can shuck when you later upgrade cases. It'll also get you more capacity for your money.
Data Hoarder
We are digital librarians. Among us are represented the various reasons to keep data -- legal requirements, competitive requirements, uncertainty of permanence of cloud services, distaste for transmitting your data externally (e.g. government or corporate espionage), cultural and familial archivists, internet collapse preppers, and people who do it themselves so they're sure it's done right. Everyone has their reasons for curating the data they have decided to keep (either forever or For A Damn Long Time (tm) ). Along the way we have sought out like-minded individuals to exchange strategies, war stories, and cautionary tales of failures.
You only have 1 option, what do you need advice on lol
If you go external, give yourself room to grow. I regret buying a two bay QNAP das to expand outside a small PC chassis.
With your optiplex 3060, you should have usb 3.1 gen 1 ports more than capable of supporting a 4 bay DAS.