A couple of comments regarding NAS storage and my experience:
1. Don't underestimate how useful a NAS becomes and therefore how much disc space you will need to store:
- Your music collection (Probably FLAC). Multichannel and stereo too.
- Music Videos (Concerts etc in multichannel from blu Ray and DVD)
- Favourite movies and TV series (I've got 4TB of war movies, nearly 4TB of historical movies and same for historical TV series)
- ISO backups of all your music discs
- Backups of family PCs, photos and other docs.
2. RAID is not backup. You need to have a separate backup disc for each NAS hard disc (external USB hard drives, in my case 4TB HDDs in a USB 3.0 cradle). Those backup discs are stored in my detached garage in case of fire or theft of my NAS.
3. I didn't use RAID at all. I used 4 x 4TB (individual drives) in my first 4 bay NAS, with 4 x external backups. I got a full 16TB of useable storage (with RAID 1 I would have got 8TB, yes redundancy, but redundancy is not backup!)
I later bought a 2 bay expansion unit for 6 x 4TB drives total. Now I'm on a 12 bay NAS...
Since I'm retired I've got lots of time to convert all my discs to digital format and store them, and back up the changes. You'll need plenty of time too.
Windows Robocopy allows you to copy 'only changes', so ideal for backing up NAS drives to external HDDs.