So - Finally I was able to set up a Friendica instance and it looks really interesting...
But I could not make Hubzilla work so far, unfortunately.

I still need to

- install and test Wordpress with ActivityPub Plugin
- install and test Misskey
- even though I deleted Pixelfed from my Yunohost I will reinstall it - it is usable, if there are only 40 photos in an account. I think I will test how fast a new account can grow if it's not on a big server
- even though I think I won't use Mastodon, I will reinstall it to test it more thoroughly etc.

It's quite a bit of work, but it's fun.