im from a selective school and i can reassure you that we are not like boring nerds like how it is often assumed. a selective school environment is like any other student environment, with the exception of the fact that students generally care more about their academic performance and their future career plans (some people to the extreme, and some people not at all). like any other large environment, there should be a variety of social bubbles that you can select from, so just be yourself!
i dont remember the NSB selection process but since you have made it in after being chosen from a pool of high performing students, it is likely that you will be at least average or a high performing student once you join. in order to perform well or maintain your ranking, of course, you will just have to work hard and be consistent with a sustainable study routine, there's really nothing unique to it.
also with the ipad question, its not really a question you can ask generally as ipad note taking is just another form of note taking, each methods has its pros and cons while each individual has their own strengths and weaknesses. you should consider the benefits and drawbacks against your own preferences!