you've mentioned that some song sessions end up at as many as 600 tracks, what does your organisation look like? do you organise your sessions to deal with that many?
the major categories for me are 'DRUMS', 'BASS', 'NON', 'VOC'. within those categories there are some sub categories, but the system starts to fall apart as it gets more ambiguous. 'NON' means any non-bass non-vocal, pitched instrument. 'DRUMS' usually means any non-pitched instrument