Thanks a lot for your current conclusion, Olaf. That’s a great post and describes very good what I try to achieve for my note management.
A few days ago I stumbled across the following new Service from Zendesk https://hypernotes.zenkit.com. I just started to play around with it and it already looks very promising. It seems to be a closed system at the moment (unlike Obsidian) but offers quite a lot of the functionality you described above. I am not sure yet, if it will replace Obsidian for me.