I asked Graham, and he said that the consensus is that the Moon Unit is structured like the Japanese Yen, but you use metric prefixes for large numbers.
Graham Stark @Graham_LRR
@robertbmtg Asked around: we’ve decided that they’re like Yen, but if the numbers get too big you can use metric prefixes. Kilomoon = 1000 (Link)
The yen uses coins for 1, 5, 10, 50, 100, and 500. There are also bank notes in 1000, 5000, and 10000. I don't think I have it in me to design that many objects, so I was thinking 1, 10, and 100 coins and 1000, 5000, and 10000 notes.
Here's my question to you all. Who should be on what value of currency? Should it be cast members or characters? Right now, I'm thinking about Spoopifer on the 1 Moon Unit coin (so many ghosts in your pocket) and Gib for the most valuable note (add a 1,000,000 Moon Unit bill so it would be a Megamoon?).
What do you all think?