Thanks for all the tips, guys!!
DollFacedDude: I'm thinking 2-3 feet--as big as I can make it while it is still functional. And yeah I'd be hiding any hardware in the poltergust's body
(and thanks for the compliment! I'm pretty excited for this idea)
animenerd93: Great idea! I think we even have one of those (and damn are they noisy) but noise shouldn't be too much of an issue unless the con has some rules against it.
verdatum: Really? I was thinking about using an old PC fan I have but I wasn't sure if it would be strong enough. Thanks for that info!
Hopefully I'll be done in time for AX. See you there if you're attending!