electromagnetism - Coulomb's Law: why is $k = dfrac{1}{4piepsilon_0}$

This was supposed to be a long question but something went wrong and everything I typed was lost. Here goes.

1. 
   

   Why is $k = \dfrac{1}{4\pi\epsilon_0}$ in Coulomb's law?

   
   


2. 
   
   

   Is this an experimental fact?

   
   


3. 
   

   If not, what is the significance of this definition?