Sorry for responding so late. I have used the time to make some experiences with MusicBee and adapted it to my needs. However, I could not solve the most problems.
1. Sorry for the missunderstanding. I use only (!) ID3v2.3 tags within mp3 files. Meanwhile I had the request from MusicBee if I want to save changes - but only sometimes. Until now I do not understand when it asks and when it just loses all changes.
2. Yes, I set up MusicBee to scan the folder continously.
Here is a screenshot with that warning sign:
For those who do not understand German: The mouse-over text means "The processed file(s) was/were changed outside MusicBee - maybe it/they have to be memorised again to ensure that the newest tag data are shown and saved."
Is it possible that MusicBee needs more time for large libraries? My library is 21k+ files large.
Does it happen specifically if you don't have continously monitor turned on? It's entirely possible it goes by so quickly I just haven't noticed, too.
I haven't tried it but I will.
3. That works now - I don't know why.
4. I have not yet worked on the virtual tags.
Thanks for your help