Recommendations for electrostatic potential surfaces
You have probably found out from playing around that there are many options. For coloring there is no standard, blue and red are common because they are the easiest to see since they contrast well. As far as the density cutoff, there are some papers that recommend values but the main idea is to choose a value that gets close to the Van Der Waals radius for the atoms. This is after all what is typically is of interest in a chemical sense. The electron density at the Van Der Walls surface is what others atoms/molecules "see". Typically I will just plot both the Van Der Waals and electrostatic surface and modify the electrostatic cutoff to make them close. Then you can set the limits for positive and negative colors.