NAS RAID configuration

So you're recommending that with the above equipment I could configure drives 1-4 in RAID 0 for a virtual disk capacity of 24TB (call it drive letter D1) and configure drives 5-8 in RAID 0 for a virtual disk capacity of 24TB(call it drive letter D2) then set up a backup where D1 directly backs up to D2, right?

I am wanting to move my DVD collection to an NAS device to watch them over my network. I have approximately 600 standard DVD movies, approximately 300 bluray movies, and approximately 300 standard DVD TV series disks. I have ripped a few of each to my hard drive to estimate storage capacity needed. The bluray movies and standard TV series disks are approximately 8GB each and the standard DVD movies are about 2GB each. So the expected capacity needed would be simple arithmetic; 600 blurays/TV series x 8GB = 4.8TB plus 600 standard DVD movies x 2GB = 1.2TB so approximately 6TB of storage would be needed. Is that accurate?

If the box has all those drives it fails one of the basic tenants of backup. That box holds the entire data set and if it fries all is lost. There was no backup from what I could tell.

But I do see what you want to do and if you keep all 600 DVDs that would be the backup. Sometimes you find folk that dump the DVDs as they digitize them. Eventually some event happens such as a slip of a finger and the contents are deleted. That's not something RAID guards against.
Bob

Once I set up this NAS I intend to use an online backup service such as Backblaze for a permanent whole network backup of all devices on my network. But again given the computations in my last question about required capacity does 6TB sound like enough? I will probably equip a Synology DS415+ or Synology DS1515+ with 6TB drives for future needs.