Hey, to hang out with Juliet or any future characters, you have to gift them a gift item. You'll need to earn 3 stars (in the phone contacts) for them to advance the story aka hangout. It was explained in the story but I think I can improve on that in future builds.
As for Maggie, make sure that you're in spring/summer because of her hobby. We might make it so that that isn't restricted to those seasons.