I had this same issue as you going to this event. Housing
seems to be a hassle. I asked currents/past students who were on the panel about this. In total, I directly interacted with three and none of them had or was living on-campus. They could not, as a result, vouch for the niceties/affordability of on-campus housing. All these students said was that there was nothing they could have gotten from living on-campus that they did not get off-campus. As for aprtmts/studios close to the Mailman School, well it all depends on your budget and how much time you have.
Then director of the housing office gave a talk. To be honest with you, none of the things she said assuaged my worries. Basically, the way things work, international students have priority when it comes to housing, be it on- or off-campus. People from out west of the U.S (Cali, TX, OR, etc...) are then next in line. Those from the tri-state area (NY, NJ, CT) and other New England states are at the bottom of the list. Not surprisingly, she said that her office assists incoming students regardless of whether or not they have been offered housing. Specifically, she and her staff can tell you which neighborhoods to consider/avoid living in.
Overall, I got the impression that those of us who fall into the last category will be having a tough time finding apartments. But I think that if you have friends/family in NYC (who might help you look for a place to live), time and a bit of $$$, then things might be easier for you. On the other hand, if you are like me and don't have any of these, then looking for housing might prove to be something of hassle. Anyways, we were told that more info could be found here:
http://www.cumc-housing.columbia.edu/announcements.html
I hope this helps!