What rehearsal criteria would apply to M2 also applies to any other composer's work for chorus, soloists, and orchestra, as I've experienced in my many years as a chorister, which includes M2. The number of starts and stops depends on what the conductor feels is going well or not going well with what he wants the orchestra (and singers!) to do at given points in the score. Being as the NYPO has done M2 numerous times (and can probably play it in their sleep), all it would take would be for Alan Gilbert to indicate beforehand where in the score that he wants to do different than what's indicated. With this particular work, all should go well, and a final rehearsal should essentially be a play-through with the areas of concern that the conductor feels need be given attention. Often, areas of concern usually are balances between soloists, orchestra, and chorus. I would think that you might hear the finale from the entrance of the chorus no more than twice, but I could be wrong. A work like M2 at the ffff portions of the closing pages can be hard on a chorus' voices, and a conductor would be wise to limit their number of times singing this part.
Most likely, Gilbert will have a separate rehearsal involving the chorus and soloists, and eventually dismiss them to rehearse the orchestra in movements 1-3 and the finale up to the choral entrance. I haven't been involved in an open rehearsal like you describe, though I would think there might be applause.
Wade