Thanks a lot for your answers! They are very helpful!
I guess a combination of material settings and use of brushes in Photoshop would be the best.
I searched and found the mentioned products - wow!! Definitively it's a good idea to buy something like that.
Above of this I'm always searching for knowledge and want to figure out the "how".
Thanks, LightningJynx, for your little hint.
Seems to be the best to follow the tutorial in this case. At long sight one of the other soluation is probably the best.