Arbus used a Mamiya most of the time, along with a Nikon F. She carried a flash gun. Later she borrowed a Pentax 6x7 from Hiro and her anxiety about buying one was apparently prominent during her last few months. She and Alan did magazine work from the 1940's on, so I'm sure she was at least familiar with a lot of various gear. She was friends with Avedon, Marvin Israel of course, Lisette Model,others -- the core of the NYC photo scene at the time. And Walker Evans sent her work, and she adored Sanders.
People who complain about her being exploitative have usually, in my experience, seen only a half-dozen prints or less of her work, upon which they base this allegation. But Arbus was not exploiting people -- and unlike the viewer of the photograph, she was there with them, immediate and engaged. My own impression is that she was the super master of photographer-subject connection. There are dozens of stories about it.