I think it sounds like a very cool idea-but I do think you have a point about the cereal getting soggy and turning to mush very soon. That could be QUITE icky.
A geisha costume will be super easy. A quick google search yields a bunch of sites yields a bunch of cool wigs you could buy for your outfit like here:
http://www.costumzee.com/tag/geisha+wig/
Buying a cute kimono dress will also be super cheap if you hit up China Town in Los Angeles. Top it off with some white as a ghost makeup, bright red lipstick and maybe a cheap Asian style parasol (get this from china town as well) and I think you've got a rather simple, cute costume.
Good luck.
