So my first comment about this is that you either have 8TB of unprotected storage, or 4TB of protected storage.
If not setup in a RAID configuration you risk losing a LOT of data if a drive fails. If you don't care if you lose data, then the 8TB unprotected configuration might be okay.
Two reasons I wanted a home NAS. 1). Ease of access from any computer in the house. 2). Data protection (i.e. RAID and snapshot backup). Snapshots are good if someone fat fingers and deletes a file, you can easily recover a file from snapshot backup (deleted files on NAS mounted drives will not go to recycle bin when deleted).
Drobo are popular. They just didn't have an affordable configuration for the amount of space I needed.
So I purchased a bunch of Western Digital 'RED' drives and downloaded FREENAS (it's free) and have been using it ever since.
I put the RED drives inside an older retired gaming computer and installed FREENAS. RED drives are designed to be powered on and run 24x7. Traditional desktop drives are not designed for that purpose.
Lots of tutorials on how to set it up and use it.
I also grabbed a retired disk array from work and connected it externally.
FREENAS picked it right up and now I have 51TB of storage.
I am comfortable doing this sort of thing as I am a Storage Engineer for a large pharmaceutical company....this is what I do for a living.