Simply download the blender file and put it in the a new folder then open up any Blender file and enable blender addon called "node presets" (comes with blender by default) and point to the folder where you saved this file. Next time you use Blender and want to create the material using this shaders simply press shift+a and under template you will find this shaders. This method is best used for tools, as for the shaders all are marked as assets and work both ways.

Yes, as I make new materials I will update the library.

Yes

All the values are set for the most realistic look but that doesn't mean you can't play outside of that, under shader editor simply expand the node tree and press "n" to get side toolbar and under "group" change the default values to your liking. Keep in mind that changing this might break the effect.