Honestly, with Storage Spaces you won't get any performance, as well as, reliability. First of all, parity option with storage spaces will lose your data, unless you have reliable backups.
You can try to go with stablebit drivepool + snapraid and check the performance, at least it is simply more reliable. Otherwise, to get a decent performance use hardware RAID or linux mdadm.
Look for the deals on high capacity drives. Any drive from Seagate, WD or Toshiba should work for you, just look for the best price within desired capacity.
I would use Samsung PM897 rather than 990 pro, simply because PM897 is enterprise drive, and it should be more reliable.
Also, compare both drives DWPD, the higher it is, the more reliable drive is. https://www.kingston.com/en/ssd/dwpd
Obviously the best medium to store the data is HDD, just because of the $/TB ratio. You can get high capacity drive for really cheap. Also, if there nothing special is required in terms of performance, I wouldn't look into SSDs.
I do not see any issues using not DIY NAS, as OP wants. As you mentioned, it is a data hoarder forum where people can save the data where they want.
It really depends on you. Synology is more plug and play solution which is easy to configure with the most basic applications.
If you want to save some money or get better hardware than used in Synology for the same prize than DIY NAS should be your choice. It will take some time to configure it, however, it is more customizable with a better hardware.
Look for NAS/Enterprise grade drives (they are all cmr) with the best $/TB ratio and warranty time. There is really not much difference between alternatives from different brands.
Look for enterprise or NAS grade drives. Really no matter which brand, just look for the best $/TB ratio.
I believe you just got bad luck with those drives. You should be able to RMA those drives if they were bought as new. I had a few drives which failed in a few months, and some that are running fine for 5+ years.
Restore from backups or get the new drive and redownload the movies. Other option, you may try to shuck the drive if that is external drive.
Alternatively, you may send your drive to data recovery shop, however, it won't be cheap.
Hmm.
But the question was obviously not about DIY NAS... Ok.
Hmm, het the drives, check the smart data and run the full surface test. If the drives pass the tets, you should be fine. Also, clarify about warranty on refurb drives since they usually have a limited warranty for 2 years.