How does increasing the number of charges affect the electric field strength for a given distance?

You'd have no problem with that question if I asked you "How does increasing
the amount of charge affect the electric field strength for a given distance ?  
Obviously the electric field strength at some distance would increase in direct
proportion to the amount of charge (as long as the charge is all the same sign).

Well, it wasn't until about 100 years ago that anybody knew that there was
such a thing as the "number of charges".  It was thought that charge is
continuous, just like the way we think of water, and that there was no such
thing as the "smallest piece".

If the distance from all charges is the same, no matter whether they're all
electrons or balloons, then the field depends only on the total amount of charge.