That was kickass!!! Where do you work that they fund you to build shit like that?!?
You're probably already on this, but a milar balloon will let you be able to inflate/deflate the baloon without leaking helium (it's lighter than air b/c its a tiny atom, and so will slowly wick through the rubber balloon)
Also, a smaller balloon, while not as visually rad, would be way more manuverable. The key isn't volume, its density. Smaller milar or other such material, with higher concentration/pressure of heilium means better flying ability. Pull the propellers off the plane, switch them onto some underpowered little motors, and make it heavy enough to need counterweights(the batteries?). Then you've got a virtual crane cam!
And I want that freakin phone by the way. Where did it come from?