It's generally safe, but you do need to exercise some common sense caution, since it gets pretty crowded at times. I suggest that you go with a group of people anyway.
I'm not into big crowds, so I personally avoid it, but it is not unsafe. If you can get to a reserved area like a balcony, then that's the best way to enjoy the carnival.
Los Robles is a section in the city of La Vega. At one time, it was the nicest (most expensive) area of the city, but there are newer and nicer areas now. (Gamundi is considered the best area now)
I'm not sure about the school that you mention, but I'll find out for you and post later.