I would not worry overmuch about his contract. There are certainly some significant things that are in every Navy Nuke's contract (such as guaranteed schools, the military's drug policies, etc.), but the contract really won't tell you very much about his future life in the military.
You won't find anything in his contract which sets his working hours or underway/inport ratio - these things will depend on what the Navy needs from him & everyone else in the service to keep our country free and safe. There won't be anything in his contract which tells you which ship/submarine (or even which homeport) he will be going to after he completes school - it could be a ship on its way into drydock where it will sit for 15 months, or it could be a ship that's headed overseas for the next six months on deployment. Your fiance will be allow to provide input on where he would like to be stationed, and the Navy will give consideration to his input, but ultimately the Navy gets the lion's share of the vote regarding where they send him - based on where the Navy's needs lie at the time.
Unfortunately, the truth is that your fiance will spend a lot of time at work (especially until he gets done with school and his first sea-going tour). I'm pretty far from qualified to hand out advice on personal relationships, but there are two things which fall outside of your relationship with your fiance that will contribute greatly to the success of your relationship:
#1 - Have a solid support group, wherever you go. Support can almost always be found with some of the other good Navy wives in the area. Having family that you can call or visit whenever needed (and they may be needed frequently) is another tremendous plus.
#2 - Regardless of where you get stationed, have an active life when your fiance/husband is at work or out to sea. Your career as a nurse should be able to fill this bill rather perfectly, I would think. Otherwise, volunteering and earnestly pursuing hobbies are good ways to keep the dead time from stacking up and dragging out.
As hard as it can be - as hard as it will be at times - there are many Navy marriage success stories. From what I saw over my own years of service, most of the successful ones had the two attributes above in common (in addition to starting out with a solid, well-founded relationship).
I wish you both the very best!