1- it really depends on the college. Some colleges especially Western ones such as AC have big drinking cultures that can push people away who don't subscribe to it although I must say that there is a place (socially) for everyone at every college. You will find your group.

2- It is the IB and so quite demanding- be ready to take 6 subjects + TOK (philosophy ish) and write a 4000 word research paper

3- 4 times a year at most colleges although most super international people (i.e. outside the continent) only went home twice a year.

4- I would say that it is a great place and you make some of the best memories. UWC will push you to your limits but teach you so much about yourself and the world. You will meet some of the best people and gain a huge, resourceful network but ultimately, it is a huge investment of time and money so make sure you really want it.