A few tips on getting loads of characters in a scene...

Textures, textures and textures. Reducing geometry will not have as big an effect as reducing unsuitable texture sizes.

You do not need 2000x2000 pixel images for diffuse, bunp and spec for eyes on a secondary character. Same for face, torso and limb textures.

You can collect textures and then reduce them manually using a graphics app, I recommend IrfanView for the PC. If possible, reuse textures but change diffuse values for variety in background characters.

It is possible to export characters and scenery separately from Daz Studio and combine them for Lux rendering. Makes editing materials much easier.