Simple answer you can't duplicate figures, DAZ wont let you. There is no technical reason for it. This has been a DAZ policy since C6.

But networthy is right. Just save your scene then drag and drop it back in; you may encounter clothing refit though. Carrara will quite often fit the clothes from the new figure to the existing figure.

Grouping may help but I have found changing the character name; like M4 A, M4 B, will help prevent this and make it much easier to refit the clothes if it does happen.

Poly count issues depend on you machine. Mine is an i5 with 6 gig and could handle my swamp scene fairly well; some hesitation and lag when moving cameras. If I remember right it had 5 M4s, 4 V4s, and about 11 surface replicators; plus boats, furniture ect. It was a pretty heavy scene.

What you can do is open your first figure then add a figure swing the camera around, add a figure swing the camera around, and keep adding figures till you have lag moving the camera. Something that helps in big scenes is making everything you not need for what you are working, invisable. As in put in your fist character, pose it, set it, then unclick visability. Dong this for each figure allows you to work the scene smoothly, then you can just make them visable for the actual render.

Right now I am working on a pool party scene with several genesisi and the dream home. I've made all of the dream home excluding the pool invisable, and working one figure at a time; the others are invisable. Other wise the scene gets slow; lag, and hard to work.