You should ask the Director of Graduate Studies to put you in touch with a handful of graduate students who are at different points in the program, ideally who work in your broad area of interest. Then set up times to talk with them. I'm the DGS at my institution and I put every prospective student in touch with current students. This is the only was to understand the atmosphere, what students like, don't like, what they didn't expect, etc.
BTW, congratulations on getting in to NU (not NW)