I had buttloads of mods installed for making characters look great, but the most important ones were the hair, eyes, skeleton, and skin mods. If you want the most natural looking characters, make sure you get a great skeleton and skin mod, which are complimented by a nice make up mod.
Like others have mentioned, you don't need to restart in order to re-do your main character- there is a console command, "show race menu", and you can change everything there- sex, race, body type, tattoos, facial measurements, hair etc.