What exactly is electric potential (what's wrong with my picture of it)?
Not gonna read your entire question, but seems the explanation of your book is overly complicated for no reason. When people cannot explain things simply, it usually means they don't understand them themselves.
If you relate to a cylinder filled with water that has a hole at the bottom:

The potential (Volts) is the &quot;pressure&quot; at that hole
The current (Amps) is how much water goes through that hole
The power is the multiplication of these two
The energy is the power over time.

I think this relates to your gravitational field but is handier to understand.