billions of people in history reading and studying Holy Scriptures.
billions of people sacrificing their human needs and aspirations in the name of God.
billions of people hating and going to war in the name of God.
billions of people walking in the sun around holy places for several hours
billions of people building huge buildings and statues in the name of God.
please feel free to continue the list…

I wouldn’t say energy per say rather I would ask how much time was wasted in searching for this “God” person.
simply put, alot.
What do you mean “If”? Of course gods are a human invention.
Some social cohesion benefits but, as you say, a lot of unproductive effort.
I guess we all have an ecological footprint…
None. Apply 1st law of Thermodynamics.
8.2×10^23 KJ of energy.
The Catholic Church was founded by God all the rest are man made.
Made of Embryonic is right.
Religions are a human invention,
but this is only part of the picture
God is not a bearded man sitting on a throne
but another name for the Law of Nature
The Power of Love
No energy is lost by connecting
to such source
These links can demonstrate ways
to do that:
http://www.perceivingreality.com/
http://www.questionyourreality.com/
http://www.illuzia.net/