I think we need tags for discussions about the Path and The Fruit and the stages of Sainthood and Fruit of Attainment. There is a tag for stream entry but not for the others.
I think the general principle of tagging is that people should just tag questions as makes sense to them. We can always retag if it doesn't make sense and I believe tags can always be removed entirely if some really bizzare ones crop up. I think the tags we have got at the moment all seem perfectly fair really. The good ones float to the top anyway.
I would just go forth and tag.