I wasn't in the post bac bud I went to NYU and knew a lot of people who were doing post bac. Your classes are with the undergrads for the most part and while NYU doesn't assure you of your desired schedule, they will make sure that you get into all of the classes that you need in the necessary timeline. As for the difficulty of the workload, it's NYU. It's hard. Most people get A's in gen chem, Orgo is fine if you get it. The only class curved at NYU is physics and its also notorious as the pre med dream buster at NYU. It's tough but definitely doable. Just don't let New York City distract you and you will be fine.
Good Luck