also youll have to tackle photoshop.
And if making a texture is an art by itself making a displacement is even a harder art, but there are ways to sidestep that. To, for example, make scales, by modeling 1 really detailed scale, then making a group of them positioned in a way that you later can pattern, then rendering to obtain a displacement (see art of maya or maybe its also in the f1) or obtain it trough the normal mapping trick(that last one just maybe, i think i alrready said im doing that tut when i have spare time). Then you take that to photoshop and pattern it or plug it to a brush and paint over the uvs... you can then adjust the global displacement with the displacement AND brightness/contrast(dunno it they are called like that but i know whre they are and how to use em) sliders...