Maybe a strange question, but I wonder if emptiness (sunyatta) is also a characteristic of the state of nirvana?
Actually, Nirvana... is something beyond emptiness. Emptiness (sunyata) is the stopping phase of cultivation. Nirvana is the "seeing" phase, where you transcend even that stopping, which is a type of total non-existence, still dual.
Nirvana is beyond all dualism. It is not existence nor non-existence. Heart sutra is reccommended.
Nirvana is a synonym for the enlightened state. The Enlightened state is beyond non-existence ("emptiness") and existence (experiencing the skandhas) and is capable of existing and exercising its function anywhere, no matter what, be it in hell or heaven. N onetheless, we must experience both sides fully, existence and non-existence before we can enter into the non-dual, indescribeable, open awareness of Nirvana.
Note: despite this, emptiness is still the first step, especially in this age where everyone is obsessed with materialism and existence. Finding emptiness IS the first step. You must make your mind empty and clear and must discover and BECOME emptiness, particularly through attainment of samadhi before you can truly succeed on the vipassana path. Of course, others have differing perspectives saying that "dry insight" is enough to get to Nirvana but I don't think it's that easy or even reliable as a path.
Calm your mind (emptiness, samatha practice, focus your mind on clarity), and see (Nirvana, vipassana, let go of everything and just witness).