1. Afraid you'll need helium, lots of it, and it isn't exactly cheap. In the US the stock exchange quote is around 60 dollars/ one thousand cubic feet. Dunno about customer final bill for bottled helium.
2. Depends on location, if you are on an approach course for an airport forget about it... but you may ask the Civilian Aviation Authority about safe heights and location. I presume you need to notify the presence of the balloon. Contacts may be found under the thread on searchlight license.
Andrea