NAS is a good choice imo. use raid 1 to mirror the drives, this way if one shits the bed, the information still lives. I have an old dual core running my NAS with 4 drives, one for the OS and 3 in raid 1 to make sure i dont lose anything. I've had drives fail before, and its nice to know its all still there.
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 basically do the other way around. Buy a NAS for your primary storage since it provides redundancy (RAID) and that you can reach it from anywhere. Then you attach external drives to it for one of the backups of the data from the NAS. The second copy should go to another physical place. The cloud or a friends house. It’s called a 3-2-1 backup strategy.
+1
RAID NEVER WAS AND NEVER WILL BE A BACKUP!
Your local external backup is for quick recovery. Your offsite backup is in the event of a local catastrophe; fire, flood, hurricane/tornado, power surge, theft, etc. that takes out your NAS and local backup.