[itsme]

to 3.)
The starting key that is set by the current key is stored per song in the database, correct? Why not keeping that database field as it is, just fill it when the file is imported (or re-imported after a change of the file)?
If "Detect Key By" does not detect what I want I add a "{key:" directive to my ChordPro file. It is not required to read the key directive every time when the file is opened. It is sufficient to read it, when the file has been changed. I think this is already the case.
The "Detect Key By" setting is in my opinion a decision that is not changed frequently. If it is meant to be used just for the very first import of text and ChordPro files, it should better be placed in the "Import Settings" dialog than in the general settings.
I do not use "Detect Key By: Chord Progression". It is not transparent for me how it works and could be affected by any chord change within a file.
If detecting the starting key of a text file detects something unexpected, the user can use "transpose by semitone", supposed it is available.