"that would be the closest you could get to proving the nonexistence of God..."

It's almost there! You might like to do some research on 'Abiogenesis'

Your questions:
I have an Art/Creative background and was never that much interested in the Sciences.
My atheism stems from a philosophical thought process but I have become more and more interested in Biology, Cosmology, Geology and the Earth Sciences - these have just reinforced my atheism.

Actually the ONLY thing that labels an atheist is the non belief in god, in my case because of the previous paragraph. And as I said earlier, to be accurate the term is a 99.99999999% agnostic.

Extraterestrial life: No one can say for sure.
The probabilities suggest it does or has existed somewhere in the vast universe, so probably.
Intelligent? Possibly, depends what you class as intelligent.
Ever visited earth? Almost certainly not, but again it cant be absolutely dismissed.

"Deaths in the Bible. God - 2,270,365
not including the victims of Noah's flood, Sodom and Gomorrah, or the
many plagues, famines, fiery serpents, etc because no specific numbers
were given. Satan - 10."