Very long-lived.
2. How many races are involved in the intergalactic war Nokkar was fighting in? What are the races?
Three races are involved. The first is Nokkar's race, the N'Kai. The second is the Space-Spawn. The third has not yet been revealed.
3. Which alien race is older, the Space-Spawn or Nokkar's race?
Nokkar's race is older.
4. Since Nokkar thought the gargoyles were evil aliens, does that mean that gargoyles are aliens, or at least that some aliens resemble gargoyles?
No. Nokkar simply assumed that, since they weren't human, they must have been extraterrestrial and hostile. (Rather similar to the immediate human assumptions about gargoyles, isn't it?)
5. Which race is winning the galactic war in 2198?
The Space-Spawn.