1.
AFAIK the engine is the same. Nismo has a different stock tune.
2. Yes. Yes.
3. Your dealer is probably just stupid. Unless it's a new thing, I don't believe you can get Nismo in 7AT.
4. Yes.
5. 1200 miles is the recommended break-in period by Nissan. If you searched, you should have found all sorts of information. The opinions on this vary widely.
6.
are you referring to a bike? Just change the oil after the break-in. Then change it at your preferred oil change interval mileage. Again, if you had searched you would have found loads of information and widely varying opinions.
7. BigAudioFan, but do your research before you ask him stupid questions. Unless of course, you're willing to pay him for his time.