I basically believe in the big-bang/evolution explanation, although it describes only the physical aspects of existence.
How the other aspects came to be (i.e. thoughts, emotions, imagination, even just perception), and whether they are older or younger, who knows.
I kinda have the theory that all these planes of existence (including the physical plane) are just different ways of looking at the same thing, or different shapes of the same thing. I don't believe in any really objective universe. Just in one consciousness fragmented into myriads of seemingly separate selves.
Satan is rather an impersonal force to me which permeates/is everything, so while it of course then is the cause of us, I don't think calling it creator makes that much sense.