The reason most professionals create a bump map first is easy. you can paint the diffuse map above the bump. For instance there are bumps and pimples, you can paint them on the same place as the bump map. I use mostly photos, you can of course start the diffuse first.

You have zbrush, Let us forget the maps first. Think about it, it is a sculpting app. You want pores, you want wrinkles( goodbye digital botox lol). Create the pores when sculpting. use the layer options to change the strength. Happy? bake them, export them as a normal map or displacement map ( you can eventually convert them to bump maps)