You want to move your drives to your mainboard because a lot of those cheap adapters suck. Unreliable and they can buckle under load. Can be a PITA.
If there is performance to gain depends on how accurate your information is, what drives you use, and how.
My backups are tiered. Some stuff gets no backup at all, some gets even more than 3.And I tend to reuse HDDs that got replaced in my main machine due to size for my backups. Power consumption hardly matters when it only runs for a few minutes a day.
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)
These old machines make less and less sense. They consume 1-200W at idle but have less power than a single, modern 6 or even 4 core CPU. So unless you need a ton of RAM or PCIe they are really hard to justify unless your power is dirt cheap.
i heard some people can 'wipe' the S.M.A.R.T data which will make it look like new? is it true?
Yes.
Archiving modern websites is rather tricky. There are tons of servers involved and they often run some software themself. These are black boxes that cannot be archived without direct help from the web admins. For this reason, archived sites are often broken in some minor or major way.
Without a link, it is pretty hard to help you with your specific problem.
£5 x 40 = 200. £3 x 40 = 120. Seems like you calculated with 20 and not 40. This helps to bring the cost down but even for 250 you can at least a single decent NUC.
As I said this is something they cannot deal well with.
Only to carry a few files or whatever from one PC to another. They are just too unreliable, get lost or damaged too easily and their performance almost always sucks.
Unless you have to have your data always available a single 16TB drive will work just fine. ~£200 for the drive and it also consumes 10W and not 40. Likely pretty relevant in the long run in the UK.
And when you need more storage use Unraid or mergerFS+Snapraid on Openmediavault. They both allow you to add single drives of any size to add storage capacity and parity. ZFS is great but it kinda sucks as a home user as expansion only works well when you add 6 or even 12 drives at a time. At least for now.
Get a NAS. Unless you are tech savvy and dedicated get a Synology. You can get another Synology or hook up a USB drive for backups.
To backup and manage your photos you might run Immich in a docker. Although some people also like Synology's own solution.
Every drive can fail at any moment. Even a brand new one. It is just a bit less likely than having a decade old drive fail.
If you care about your data make sure you have backups. 321rule.
Yes, you can use a "NAS" drive pretty much like any normal drive. This is an SMR drive so not even a NAS drive to begin with.
If you do not have backups pay a professional to recover it. Yes, this is wildly expensive but tinkering yourself can make recovery even more expensive or outright impossible.