What is your goal after the MA? Do you want to go for a PhD in Classics/ancient history, or move on to other career paths? How much ancient history did you do during your BA?

If you want to do a PhD in Classics, then you're going to need language training. Everyone I know who has done a post bacc did so to get more language training before their doctorate. Since you sound like you haven't done any languages, if you really want to pursue this as a career, then a post bacc is definitely the best place to start.

But. If you just want to do an in translation ancient history MA and end it there, then language training isn't as necessary. It'd probably be worthwhile to take some Latin and/or Greek if you can to strengthen your application. But I know several people who got into history MA programs with little language experience and then went on to do other things, like law school, government work, etc... But again, all this depends on what you want, and how much ancient history you did in your BA. It'll also be worth checking out multiple MA programs, including many in Canada, which will be cheaper than nearly all USA ones.

As for a book reccomendation, Gibbon is generally not a good first work to read. It's very interesting, but outdated completely and hard to read. Be more specific about what you're interested in and I'd be happy to reccomend some books.

As Publius Clodius has mentioned, it would be necessary to know what your goal after the MA in Classics is in order to advise you in any meaningful capacity but I will provide some input.

Are you a resident in New Jersey? It's not necessary to answer this question but I ask this because while the Rutgers post-bac looks fine, if you're not a resident in New Jersey then I imagine it'd be prohibitively expensive. I would suggest the alternative of matriculating at a nearby university with a Classics program and do the language work there (if Rutgers is nearby then disregard this spiel). With the exception of UPenn's post-bacc and a few others, I find that many Classics post-baccs will place you into their second and third year Greek and Latin courses along with undergrads.

That isn't to say that you won't get a good quality education, I would just argue that you can get a similar experience from enrolling in a nearby university and taking the language courses there seeing as you can't get any financial aid for most post-baccs (again, Penn being the only exception of which I know).