Is it meaningful to talk about the capacitance and voltage of a single electron? If a charged sphere is said to have a certain self-capacitance, dependent on its radius, then could a single electron also have a specific capacitance value, and since V = Q/C, a specific voltage?  
 A: The field around a charged particle (like an electron) is associated with
voltages (electric potential) in the familiar 1/R manner.   In a sense, all charges are measured by sampling the field (i.e. voltage gradient) they
create.   So, yes, a single electron does have voltages associated with it,
because it induces voltages in its vicinity.   It cannot, however, be
identified with a particular voltage value, unless 'infinity' were
such a value.   One cannot remove part of the electron charge, so it
cannot be said what energy it takes to do so.
As for capacitance, that is (dimensionally) a distance,
and not a property that is directly connected with the charge or mass of
an electron.   In a sense, a single electron just doesn't have a particle
property to derive capacitance from.  So, there's no capacitance of an
electron.   One cannot ADD a new part to the electron charge, so it
cannot be said what energy is stored when one does so.
A: This is something that has confused me before when I started to think about it.  The way that it seems is that when electrons are stationary in a material (an object with static electric charge whether it's a piece of styrofoam or a capacitor), the effective charge is dependent on the number of electrons and their voltage.  For an electron effectively alone or in motion, the charge is defined as just the elementary charge of the electron(s).  As for single electrons, maybe they could be hypothetically viewed as charged spheres with a constant capacitance and voltage, but that's purely hypothetical as electrons are not shaped like nor do they exist like billiard balls.  The arrangement of electrons seems to be just as meaningful for charge calculations as electrons themselves.
