Hello,
I'm not OP, but I am in my last semester of the Post Bacc program at New Paltz. I applied to grad school this application cycle and was accepted to 3 schools in NY. I'm in a slightly different position than you, as I took some prereqs during undergrad - I only needed 3 classes total to complete my prereqs. However, I did take 2 courses last semester, and I found it really overwhelming. However, that had a lot to do with one specific class - the Observations course. They have you do either a writeup on a few observations sessions or a mandatory discussion board on alternating weeks. There's something due every single week that class. It didn't help that my TA was a particularly harsh grader. The other two courses that I took were much easier to manage. Oh but I should also mention that I was working full time while taking the courses, so that definitely had an effect on things as well.
I can't speak on letters of rec, as I got mine from my undergrad professors, but I had a friend in the program who obtained one from one of the professors in the post bacc. If you're planning on getting a letter, I would recommend interacting with that professor a lot so that they get a sense of who you are.
Going to a wedding your first week should be fine - just make sure you check your syllabuses to make sure you get in everything that is due. As for the textbooks, you could find textbooks in both physical copies and ebooks - however, physical books tend to be cheaper since you can find them used. I hope this long winded post helped somewhat, haha! As long as you do well in the courses, I think the post bacc program is a great way to jump into the field and eventually apply for grad school!