“Simple Sabotage Field Manual” by United States. Office of Strategic Services is a historical publication written during the early 1940s, amid World War II. This manual acts as a guide for ordinary civilians to conduct simple acts of sabotage against enemy operations without the need for specialized training or equipment. Its main topic revolves around promoting small, accessible forms of resistance that could collectively disrupt the enemy’s war effort.

https://www.gutenberg.org/ebooks/26184

dont know Yunohost

CasaOS is not an operating system and more like a GUI for Docker with access to the terminal via said GUI (at least thats how i used it)
I personally think thats a very good option if you simply want to use an old PC to host stuff and test around but its limited in its scope so if you want things like RAID you need other or additional solutions

TrueNAS is an operating system Might be overkill for a newbie and i think it was ressource intensive but offers a lot of features in return like RAID

Cant really say more because i did not visit the websites recently

At least for me its not important what kind of person he is.
I quite like that a very influental person in the gaming sphere promotes linux gaming.
Because more users means more content and support