If your a good college basketball player (or on rare occasion high school), NBA teams will look at you and can draft you in the NBA draft (when all the NBA teams pick players from college or highschool).
You do not have to go to college at all in order to become a NBA player. Most players are picked from college teams though.
Obviously, there are only NBA teams in the NBA, not college teams.
NBA players live all over America. I think that most of them live near their teams, though.
It depends. On an nba team they have 15 players. Usually on highschool and college teams theres about 12.