1) Setting up a RAID array isn't that difficult and it makes for more reliable storage.
2) Using dual supplies actually lowers the fan noise because the supply running at half power generates less heat than one running at full power. You can plug them both into the same outlet strip :-)
3) These things have a "lifetime" which is the point where things are easily found on the web which support them. And then they become "anchors" without all that support. Very carefully and diligently download and archive all of the necessary software, drivers, manuals, and extra cables for the system so that in another 5 years when it breaks you can reconstruct it successfully.
If I really need data backup, I can use one of the other SSDs or even the single spinning disk I put in as a backup target.
2) That's interesting, I don't think the noise comes from the PSU though, mainly the six case fans.
3) True point. I'm not too worried. The machine is fully supported by Linux (no drivers required) and the latest SPP is applied. I never expect to do hardware changes/upgrades down the road. And in five year's who then lives, deals with the shit ;-)