Thank you very much to take the time to explain the technical details in such a didactic way (and to
Talcum Powder and
Alley_Cat for the complements). I really appreciate!
I thought that the problem was in Daz itself, like it had some sort of limitation in rendering characters (in terms of rendering time).
Instead, if I follow your explanation correctly, no matter the number of characters (or props, for what matters), what really counts is they representation in terms of maps rather than a pure geometric representation: I may over-simplify, but the flat surface of a table, e.g., can be represented by a simple geometric primitive (e.g. 2 triangles, 1 quad) and the associated maps or by many small triangles that capture the fine geometrical details of the surface (e.g. scratches, irregularities etc). The first one is much faster to render than the second, still giving a comparable result. Plus the lights and all other sort of effects are another factor that can increase the time. Is that so?
So my hypothesis about the number of characters can be scratched. I guess the only "limitation" is the time and work it takes to animate them (change of poses etc) during the creation of the scenes, especially for a perfectionist that does not want to show people in the background of the scene as static objects