Malossi167B
It is impossible to fully eliminate the risk but with a decent backup system in place it is somewhat unlikely to lose all of your data.
The 321rule should be used as a baseline. Your local backup should be snapshotted and somewhat hardened against ransomware (pull backups instead of pushing them, do not mount the backup volume to other machines). Cold backups also help.
Can I construct scenarios in which I lose all my stuff? Sure. But in those, we are either in deep shit anyway (CME, some big astroid) or it is pretty unlikely (targeted hacking)
i heard some people can ‘wipe’ the S.M.A.R.T data which will make it look like new? is it true?
Yes.
USB is even cheaper and far easier to find these days.
Snapraid is only for parity. If you intend to pool up your storage you need something else like mergerFS on top of it. But if you care about performance it is not really a great option.
i5 processor
What i5? If it has an iGPU you most likely should remove the 970. Will just needless eat power and PCIe lanes in this setup.
setup both hard drives as a raid 1
You mean RAIDz1?
I would consider something else than TrueNAS and ZFS as a home user. It is a robust OS and file system but usually not the best option for most small home setups. mergerFS+Snapraid or Unraid are far more flexible as they allow you to add single drives of any size down the line. The performance and reliability are usually good enough for a home user with a 1, or 2.5Gbe network.
Once your system is setup tinker a bit with the OS, setup some file shares and once you know how to set up everything properly copy your stuff over and verify afterward if it was done correctly. Not really a big deal.
Data recovery is not really something you should DIY unless you are fine with losing the data. Chances are high you will make professional recovery more expensive or outright impossible by tinkering yourself.
Your best bet is to make a disk image. For this the HDD will be read like a vinyl record from beginning to end. For a file copy the read head usually has to seek around a lot to read all the file (fragments) bit by bit.
Backups and even accessing files can be a bit of a pain with two OS. NTFS drivers for Linux are a thing and they mostly work but I would not overly rely on it. For this reason, I would consider using a NAS for storing and accessing your files. It can also handle your backups with Rclone.
One of the strong suits of USB is the downward compatibility. So it should work. But check the description of your enclosure.
You can run a 990 Pro without a heatsink but be prepared for thermal throttling when you use the drive a bit more. TBH getting a 4.0 case is kinda pointless without a heatsink
Automating and streaming backups is definitely the way to go. Otherwise, it is really likely your backups are outdated and/or incomplete.
Please add the capacity of your drives. Upgrading to fewer, high capacity drives can be well worth it.
Not a bad idea although you can move files even while the drive is still part of your merge. Although this can put some extra strain on it.
If you want to be as gentle as possible a full drive image is usually your best option unless the drive is mostly empthy.