We do not have a complete understanding of how the Universe was created, nor what happened at the exact moment of the Big Bang, but we know what happened a few nanoseconds after it. All the matter was at that time just super-heated sub-atomic particles of some kind, which coalesced over a long period of time into what we know as matter.
I am not going to answer each question, since most of them are redundant.
Suffice to say, to an Atheist like myself, God is just a made-up fairy story created by mortal beings to help them to justify their existance. Christians believe in some sort of afterlife so they don't have to deal with mortality. And remember, before Judaism, people were believing in all kinds of religions that are far older than Christianity. Why were those religions wrong? The Greeks and Romans were pinnacles of advanced societies, yet their religions consisted of many different gods, goddesses, monsters, etc... Monotheism is a pretty modern thing.
Anyway, a lot of your post is philosophical in nature, and thus cannot really be explained with the science of today. However, we are getting closer all the time, with an answer just around the corner. Those few nanoseconds after the Big Bang are simply unexplainable due to the fact that today's science isn't up to the task of peering into an area where physics is completely turned on its ear.
God couldn't have always existed, since He never existed in the first place.
The Universe couldn't have always existed because we can actutally SEE what was happening very close to the beginning of time. On the flip side of that, we know the Universe exists because we are living in it. We can see/hear/taste/touch/smell the Universe. Matter, for the most part, is observable. God is not. Everything, and I mean EVERYTHING except for those first few nanoseconds of the Universe's existance can be explained by science. We no longer need to fill in the gaps with stories of a higher being.
Face it, we are, as a species, out-growing our need for a deity. I don't really know if that is good or bad, but I do see what religion is doing to the planet, and has been doing since the Catholics took over Europe and Islam started converting with the sword.
As a side note, please acknowledge the fact that I am not one of those idiot liberal Atheists that want to tear apart our Christian culture. Whenever I hear stories about Christmas being taken out of something, or someone not being allowed to display Christmas stuff, it REALLY hacks me off. These militant Atheists are anti-American losers who don't know what they are doing to our culture when they do this P.C. crap. Oh, and by the way, I voted to put the 10 Commandments up at our local courthouse. The measure failed...