Blahtor-
It is certainly okay to shoot at a higher frame rate-if you can get some decent lighting. If I were you, I would try to get at least one more light, put it behind the actor, and aim it at the green screen. And of course keep the light you already have aiming at the actor.
Then shoot at the 1080 30fps your camera offers. I wouldn't sacrifice video resolution for a higher frame rate. HD 1080p/i will give you more room to work with when pulling the key and it will make your job a lot easier. Not to mention you'll have more detail to work with when you do rotoscope work (which will be minimalized if you use the advice above).
Grant Swanson
Visual Effects Supervisor
Video Apex - Minneapolis, MN
videoapex.net
