Question 1: As far as you and your fiance... unless she changes status to your wife before going, you won't be living with her. You will be living in the barracks, and if I recall... you won't even be able to bring her to your barracks room. As far as how life is... expect to spend a large majority of time in school. It's not easy. I was single when I went through, but I was not the greatest test taker in the world, so I spent many days in at school at 0500 and leaving about 2300 taking breaks to eat and smoke. Life got easier for me in prototype because the worst that I had was 12 hour days. Keep in mind that this sounds rough, and it is, but it is rough so that you are prepared for what comes after: life on a boat.
Question 2: A school and Power school are in Goose Creek South Carolina. There are 2 prototypes just down the road as well. However... there are also 2 prototypes in Saratoga Springs New York that you could be sent to. On a bright note though, in prototype you are giving housing allowance and get to live out in town, so your fiance could then live with you, if she is not your wife by then.
I hope this helps. I do not regret being a nuke, I've put in a lot of hard work to make everything of it that I can. When you get done with school and qualifying on your first boat... you will feel like you have really accomplished something. I felt it again when I qualified EWS (Engineering Watch Supervisor).