That's a pretty big question!
Realistic materials?
Well, my advice is; realism comes from the interaction of three things;
-the surface attributes of different parts of your model (maps for colour, glossy-ness and so on)
-lighting (probably with some of it sharp and direct, and some diffuse and multi-directional as if it's arrived at the model by bouncing around on or passing through other things, )
-the fine details of the model (tiny displacements, bump and normal maps)
In practice this means examining a real object made from the material you want and trying to reproduce each of the types of surface information.
Some good starting points might be;
For metals consider what is in the environment around it. Either build a scene for it to reflect through ray-tracing or make/find a suitable environment map. (I'd guess dark wood colours and a window for your subject) Is the metal dirty or grimy? A dirt map would add realism. Most metal objects aren't perfectly smooth.
Leather's appearance comes mainly from the shape and distribution of reflection highlights. (Specular or bright areas of environment ). A high detail bump map and a low diffuse/high specular material is a good approach.
Wood is mainly diffuse colouration (high detail colour map), and bumps (maybe based on the same map as the colour).
Can't help with choice of renderer, as I haven't used v-ray. Have a look at some galleries to see which is used most successfully for the things you'd like to do.