Really Cool, Solar Powered, Balloon Carried, LED Lit, GPS Tracked Project

Hey everyone! I have this pretty sick idea for a project, but I need some help with the details. Basically, it's a cube tied to a balloon, and inside the cube, there is a GPS device, back up batteries, LEDs (sticking out through the sides), a noise maker (the one from Make Magazine #14, will explain later), a cell phone, a cell phone charger, and instructions. Also, I will hope to have the cube be solar powered. So, what I will do is send off the balloon with cube attached, and the wind will hopefully bring it to someone, but if it doesn't, not to worry, the LEDs and noise machiche will catch peoples attention. When someone finds it, they will read the instructions, and continue the chain. Here is what I need help with, having basically no electronics skill: 1: Where can I purchase balloons that are really thick? 2: How will I make the cube waterproof? 3: Right now, I'm pretty sure that the smallest trackable GPS device is a cell phone (being tracked by Mologogo). Is there anything smaller/easier? 4: Would a solar panel be able to power everything in the cube? 5: How can I wire it so the batteries can power the cube when there is insufficent light, and the solar panel can charge the batteries when there's light? 6: How do I put it together? 7: Is there anything I'm overlooking? 8: How's your day going?