Hi,
I am an Industrial design student and I am participating in a project that involves flying helium inflated balloons to a height of up to 50 meters, in order to gather people and attract crowds.
I have a few aerodynamics related questions and i'll be happy if any of you guys can help:

1. What is the best shape for a balloon, that can reach up to a height of 50 meters, and will be able to stay up in strong winds in an urban environment? (around 3-5 cubic meters)
2. Should the body have certain of fins in order to stabilize it? What should the material (if so needed) of the fin be made of?
3. What would be your recommendation for the material used to make the balloon?
4. The balloon would be anchored to the ground, with a cable, and will need to carry a weight of about 3-4 kilos.

thanks,
Idan