The good news is that it is a 9-12, so even if a bunch of kids came from the same middle schools everyone is in some way finding their way.
The fall sport is a great way to find their people. Joining clubs can be hit or miss I have found, depending on how organized they are by the students or faculty.
Socialization can happen naturally in classes as students start preparing for tests or reviewing material, etc.
Give it time and good luck!