plastic or paper
plastic
The mor the better
At least 2 liters
The mor the better
3 t05 fins
The angle of the rocket. The amount of water in the rocket.
no
If you have leaks in a water bottle rocket, the pressure will quickly escape along with the water and the rocket won't be able to reach as high an altitude as a rocket without leaks.
A regular rectangular shaped fin makes the best flight time.
KFC.
Derelict
Yes as it control the dirctions of the rocket.