Does the vertex count of a mesh affect the size of the normal mapit generates? I would like to understand a thing related to a question I asked a few days ago. 

How can you create detailed low poly meshes?

In the answer the user hawkenfox tell me 5 steps from high poly mesh and low detailed poly mesh. 

In the third point he writes "Unwrap the low poly mesh, and bake the high poly model's normal onto the low poly model. - affectionately known as "texture baking"."

My question is: will the number of vertex of the high poly affect the weight of my normal map? In other words: more vertices will be and more Mb will have my normal map or these things doesnt affect at all?
No, the vertex count of the mesh you're baking has no effect on the size of the baked texture. The only thing affecting this is the target texture (the one you create in the process of baking) size.