Realism will come as interaction between your light and your materials. So serious study of lighting - maybe from a photography book - would probably be your best bet.

But to answer your question directly - displacement is like bump mapping except the normals of your object's geometry is deformed or displaced. Use displacement map enables this feature.

To see the effect of Smooth Polygons, load a sphere and pull the camera so you can see the edge. SmoothPolys off, you'll see facets; smoothPolys on the facets are gone. I think it works by softening the normals.

Among your filter types, Sinc will give you the crispest look, though you could run into difficulty using this filter on high frequency procedural textures . Gaussian is soft looking and works well with animation + motion blur; box is a fast filter for draft quality renders.