I'm not in anthro nor a librarian, but I am a prof at UHM, so I can offer at least some advice.
First, as far as evening courses, I would say based on my program that's unlikely. UHM is a regular Research I university, and we expect our grad students to be full time grad students. They don't work and attend class at night. You can check out course schedules for the past couple of terms here:
University of Hawaii at Manoa - Class Availability
I'm not sure if you know that UHM also has a big library science program. (The department of Computer & Information Systems includes a Library Science program.) I suspect this would make it harder to find library science jobs in the area, since UHM grads might want to stick around and take the jobs that are available here.
The best thing to do is probably to contact the department and ask them your questions. (If there's a particular prof whose work interests you, that's a good place to start.) You can also find the list of subject-area librarians at UHM here:
Browse by Subject | University of Hawaii at Manoa Library They might be able to answer some of your questions about work stuff.
If you currently live in NYC, then you can expect pretty comparable housing costs, I think. (In other words, expensive and small apartments;. On a grad student income, you'll probably be sharing a place.) If you're coming from someplace in NY state but not NYC, you may be in for a bit of a shock. A good way to get a sense of housing price would be to check out the Honolulu Craigslist. Do a search for "UH" to get a sense for the costs of places near campus.
For food, you may spend a lot more (if you eat lots of package / prepared foods) or about the same (if you eat a lot of fresh fruits & veggies and can find a way to frequent farmers markets). For gas, the cost per gallon is typically more than the mainland, but you drive a lot less on a small island, so you'll probably spend a lot less for gas overall. Depending on where you live, you may not even need a car. A lot of students get around by bike and bus. (And in fact, I do too. I have a car for weekend trips to the North Shore or Kailua, for grocery shopping, etc. But I hardly drive it at all during the week.)