Thanks for your great advice! I did a quick measurement of the noise spectrum inside the cabinet with my phone:

It seems most of the noise is in the 100 - 1k Hz range.

Basotect looks perfect! It is also quite affordable. Will 3 cm will suffice or would you recommend thicker padding?

(If I can’t find a proper solution for the cable ducts, I could use any remaining Basotect, glue it together and fill the duct with it. There will be just a few cables that have to leave the cabinet anyway…)

Of course, I will do a follow up afterwards :)

I beg to differ and say, even when the Arch wiki is a great source of knowledge, setting up own Arch system and maintaining it requires keeping on track with updates, to understand what is wrong with your system to look up the right keywords and so on. In my opinion it is better to stay on a stable, periodically released distro with tested repos like Debian, Mint or Ubuntu at first. Afterwards, you can still switch to Arch.

And therefore it should not be recommended to Linux beginners… It is not a beginner distro.