I think I'm going to make a group with group owners later.
I will notify, for group owners:
group owners aren't actually necessary for groups
so if people are going a bit out of hand with being group owners, instead I will set the group to have no owner
- in which case you'll have to ask me instead, whenever you want to update anything (I'm happy with doing this)
You need to have people's permission before adding them, as you've probably seen. It's okay if they've already signed themselves up to a tag list which you now want to move to a group instead — they wished to be tagged.
And people need to be able to leave when they wish, unfortunately this isn't a separate setting for all groups.