Hi Sally,
Congratulations! I am in the MS CEE department as well. I recommend living in either Escondido Village (I am in a highrise) or Rains. EV is the cost efficient way to live, and Rains is more of a party oriented place. All of the on campus living is great because of the price for the area and the ease of getting to class. I bike everywhere, can go home in the middle of the day to eat, study, change, etc. I would say most grads live on campus. Plus, it makes group collaboration a lot easier and when you get into the program, every minute of not commuting counts as time you can be getting work done.
It is very easy to meet people, especially the first orientation week. Just try to be as outgoing as possible and you will make tons of friends. The people in the CEE department especially are very friendly. As far as recreation, It's up to you. There are exercise classes you can take for credit, or audit. My first quarter I was in intramural soccer, taking a yoga class, rock climbing on campus, and hiking the dish (a nearby walking trail) every week! This quarter I am taking tennis as a class and joining more IM teams. We also go out and play in the grass on sunny days.
Feel free to ask more questions. You are going to love it