I would get multiple drives and do RAID. Here’s a helpful calculator to figure out drive quantity, size, and configuration. The reason to do RAID is redundancy. Hard drives will fail (even NAS branded drives). You do not want your photos, media, etc to be lost in that case. I personally do not go with anything below RAID5 (and for super sensitive things, I’ll even go RAID6 - despite the hit on overall capacity. If the optiplex has drive capacity for multiple drives, I strongly recommend you go this route.