The good thing is that at Caltech everyone has to love math/science. Those that don't usually end up transferring.
1. Yes, to a degree. Some people are downers wherever they are, while other people are always able to get things going. But for most people in the middle, environment is a large factor.
2. Depends how your social life was earlier. Caltech's a lot of work, so for some, it'll be a worse social life than in high school, while for others, who may not have found people who shared their interests in high school, Caltech would offer a much better social life.