4: until the girls have any sort of meaningful development in the story, adding more content with people who are neither the core 4 nor even girls is basically the worst idea yet.
If they can get added later in the story after we have plowed the core 4 at least a few times to have some story content fair enough, but right now I can't imagine any reason to spend precious dev resources on things that aren't getting the core 4 into a playable state.