Sony Alpha NEX-5N : Questioned

Is the Sony Alpha NEX-5N considered as four thirds or micro four thirds? From what I've read, the NEX was said to have a bigger sensor. As for lenses, does the NEX have its own or can I use a different one? (eg, Nikkor and other lenses) and lastly, if its not included in the four thirds category,  what is its advantages over them?

1. APS-C sensor is the same as with DSLR but mirrorless
2. It has its own E-Mount lens. There's a Sony adapter to use Sony Alpha mount lens and there's auto-focus
3. There is also an adapter for legacy lens
4. It all depends on where you're going to use it.

I will just give a slight correction to number 1 and give some answers on number 4. That number 1 statement is a generalization. A DSLR does not necessarily sport an APS-C sensor. It may sport a Four-Thirds sensor or a Full-Frame sensor or a Medium Format sensor. The difference between a DSLR and a mirrorless is the mirror box sported by DSLR cameras whereas the mirrorless obviously does not sport a mirror box, the sensor does not matter in this case.