/3/ - 3DCG

>>478435
Throw that thing in Zbrush, subdivide it a couple of times and use alphas (the ones that come with zbrush, nothing fancy) to sculpt some bumps into it. Then you can Use Zbrush itself to bake the normal map from the highest subdivision level to the lowest, it's really fast and easy.
Get more references like pic related, I just typed frog skin in google, and try to do something like that.
When you have a more detailed skin almost whatever crappy texture you throw on top of it will look somewhat good.
And don't worry about Unity, the standard shader that comes with Unity 5 should have everything you need to achieve something realistic.