The most authentic opinion is that Laylatul Qadr can fall on any of the last ten nights. So to really be sure to catch such a night one should worship all of the last ten nights. After that is more likely to occur within the last ten odd nights. Regarding the 27th night then the majority of scholars agree that it is more likely to occur on that particular night if it is to occur in any one particular night within the last 10 nights.
Many scholars also say that it is more likely to occur within the last 7 nights. Others say that it is more likely within the last 3 odd nights. The main thing is that we "search" for it within the last 10 nights and that is what Allah wants from us because if he specified the night then we would only worship on that one particular night and not the remaining nights. But still there is no guarntee that Laylatul Qadr will fall on this one particular night.
Therefore we should worship all of the last 10 nights or at least as many as we can so that we may be of those fortunate ones who find a night better than over 83 years of worship and forgiveness of an entire lifetime of sins. We should not be satisfied with worshipping on one particular night and think that we have found Laylatul Qadr. But that we search for it within the last ten nights by worshipping on all of those nights and that way we can be sure that we caught this blessed night.
Regarding Nawafil prayers then there are no limits to the amount of nawafil prayers one can pray from after Maghrib until Fajr. The following article will help you to maximize the remaining nights of Ramadan: