Great suggestions.
Re the last point about storing and retrieving custom flush lengths.
I had a go at doing this on a mac with the keyboard maestro macro app if it is of any interest.
Its a bit cumbersome because the macro needs to go through every virtual extruder to build a table of currently configured filaments before saving or restoring manually set flush lengths but it did seem to work.
Published just a very simple one to see if there was any interest - but as there didn’t seem to be didn’t go any further.