This is missing one of the finer points of redundancy: With 4 disks, losing two of them could take out a RAID-10 (both halves of a stripe component), but losing two cannot take out a RAID-6.
The fact that btrfs isn't stable after 15+ years for parity setups is, IMO, unreasonable.
earlyoom is what we use to address this. We can't tolerate any kind of swapping at all in our workloads, where it is better for the system to kill one process to save the others, than for the system to slow down or lock up.
It can also mean that on the way down. At a private unix software company in 1994, the rise of Linux destroying our business led to firing nearly everyone in support except the cheapest person (me). As I was the only person left in tech support, I became Director of Tech Support by default.
I have posterior tibial tendonitis, and will never run (or walk without pain for more than 10 minutes) again. I am happy for you, in a bittersweet way.
Just because you can't find a useful purpose for an old computer doesn't mean they don't have any. For example, any computer, regardless of age, can be used to write a novel.
While the picture isn't technically incorrect for an MPC level one (https://en.wikipedia.org/wiki/Multimedia_PC) system, it borders on anachronistic because, as you note, many hoops would have to be jumped through. Any 386dx-33 or 486 clone would be much more period-correct.
Most Tandys with 8-bit ISA slots could not take a VGA card because the internal graphics chip could not be disabled. It was only the later series where that became an option.
The fact that btrfs isn't stable after 15+ years for parity setups is, IMO, unreasonable.