How many UVs should a model have?

Question

3D

Hello everyone, sorry for the noob questions)
How many UVs should there be on a game model and does it somehow affect the optimization?
Let's say a sniper rifle is being modeled, is it better to do everything on one scan, or, for example, a sight separately, the main part separately?
And in the future, for animation, do I need to divide the model into separate meshes?

Answer 1

Best of all, one so that when rendering several times, shaders and attribute sets are not switched.