I’d suggest you move toward a backup approach (“RAID is not a backup”) first. Assuming you have 2x10Tb, get a 3rd and copy half of your files to it, disconnect it, and now half your files are protected. Save, get another, copy the other half, now all your files are protected. If you’re trying to do RAID on USB, don’t, you are already done, otherwise (using SATA or better) you can proceed to build your array in an orderly fashion.
To a large degree, the point of RAID is to not care about drive reliability, trust the process. Also, you seem to conflate RAID with backup (“RAID is not a backup”), you want both. In a NAS, you’re probably better off with RAID5 + backup.
In a system that can take a drive failure, the current datahoarder zeitgeist is Manufacturer Recertified (Enterprise) Drives, see ServerPartDeals.com if you’re a yank, other countries have their own options.