Good Evening, and welcome to the adventure. I'm not at NNPTC anymore, but left there fairly recently (last June) so can answer some of your questions.
1. Officers enjoy a greater level of freedom than enlisted students. We treat you as though you're a bit more responsible, and housing reflects this. Married officer students can and do live in base housing, and this is a good thing, as you are very close to the exchange, commissary, school, gym, etc. Single Officers generally have to live on the community, but are paid a housing allowance to help with the expense. I recommend rooming with one or more of your peers.
2. Prototype input is solicited, and of course they try to oblige, but in the end, there are only so many spots for each location. I believe that married students who want to stay in Charleston have an advantage, as it's more economical to let them stay in housing than to move them out, and have to refurbish the housing for the next arrival. Class standing is also a factor.
3. Enlisted sections start every 6 weeks, but I thought Officers classed up every twelve. A little help here? BUT, your security clearance must be completed prior to classing up, so if you're coming in on waivers, or there are questionable skeletons in the closet, you might be obliged to wait a cycle.
4. NPS is harder. The material doesn’t have a higher level of difficulty, but the speed you are expected to consume it is an order of magnitude up. Expect long days, and long evenings studying. Get out on Friday afternoon through Sunday mornings, but expect to spend every night before an academic day in the schoolhouse studying. You'll build a routine quickly enough, and there is plenty of help available.
I hope this helps, and wish you the best of luck as an Officer and a Nuke.