B Why is the Ampere a base unit?

It's easier to measure a current than a charge.

 

This may change, wiki article:

http://en.wikipedia.org/wiki/Proposed_redefinition_of_SI_base_units#Ampere

 

And there are also a number of other reason. One very important property of the base units is that they are technologically/commercially important.. People forget that the SI is mainly a practical system for use in our everyday lives (which is why the Candela is a base unit) ; meaning practical considerations are more important that what is most satisfying from a philosophical point of view.

The re-definition of the SI will see the Ampere (as well as a few other units) be re-defined, but it will still be the base unit for the electrical units,

 

Ampere is simply related to Coulomb, although not as unity. In a real life and especially in techniques, charge is used to describe static effects, which without strong isolation and shielding are not constant, because of a various forms of leakages. Much easier and cheaper is to stabilize dynamic situation of charge flow, ie electric current measured in Amperes. Additionally, charge flow generates most effects of electrodynamics, including energetic and "electronic" we are surrounded.

 

The amount of charge a battery can energize is an important specification. It basically tells you how big the battery is or how long it can last.

 

And usually you get this specification in an albeit convoluted form, the "Amp hour", all though on its own this is quite useless, typically you also want to know how many joules you can get out of each of those charges...

 

If electric charge (the physical quantity) is not used to describe static effects then it's easy to measure. Multiply current by time.