I'm sorry for the delayed response, but work has been crazy and I just haven't had time to log on.
I can't say I measured the mini wedding cakes, but the one below was ordered for my mom and you can kind of see her hand in the picture. Hopefully, that can help give you some perspective for size.
As for an Inside Out theme...can't say I've seen one, but I have an idea that could be easily done IF they have access to an edible image of Joy. Hope this makes sense, but this what I'm picturing.
- both tiers iced in the light green like Joy's dress
- blue bursts piped on to the green to be the patterning in Joy's dress
- yellow piping around the base and middle for the color of Joy's body (or one could yellow and the other richer blue to symbolize her hair)
- edible image of Joy standing up on the center of the top tier
- a few fondant balls around the edible image of Joy - aka Memory Orbs