Thank you for all the replies.
Concerning Q. A, I'll do the updates manually. That's not an issue.
Concerning Q. B, The "Band" and "Conductor" fields are there by default. Maybe the tag format.
Concerning Q. C, It is possible that TagControl does not save proper Vorbis tags. But as mentioned, no more FLAC for me.
Concerning the suggestion of using MC for tagging:
1 - I've gone around a bit to find good tagging tools. Yes, MC has much better features than most. However on a few points, I prefer TC.
2 - For example, I've set MP3 input in MC to remove ID3v1 tags on import, but it sometimes misses them. Additionally MC captures the <comment> tags of ID3v1 if it finds none in ID3v2, sometimes creating unwanted information in the database. I do not know in MC, how easy it is to find out if ID3v1 is present and how to manually delete just these tags.
Cheers,
Sar.