I think null safety is an important step into software security. I like any approaches in that direction. But personally, I would just use kotlin. Kotlin and Java are so good with Interoperability that the transition is quite smooth and easy. Furthermore you get a better and more modern programming language without decades of technical dept.

The german wetter.com has that feature.

I have a personal wiki instance hosted for that purpose. I collect knowlege in it, that I might need later and forget. Although I might not use dokuwiki, if I had so start the wiki again (would go to markdown).

Restic

I have one setup. The setup was abit clunky since cli work is required. But after that I had a great experience.

I have markdown files in a git repo and run mdbook via cicd so I get a nice html build. Localy I can build it too or just use the markdown files (except for mdbook specific features such as preprocessors).