Your collective assumptions effectively presume your conclusion. Does any biologist say that what you are postulating is what happened?
Why would you look into that, when you can "refute" evolution so much more easily by simply inventing your own model and then beating the tar out of it? There's a term for that sort of argument, come to think of it, but it slips my mind at the moment...
Oh, yeah - now I remember...
I know it may be hard to believe, but I am a scientist...no kidding, degree and everything. Change the assumptions, collectively or individually, as long as they are reasonable. Then recalculate the probability. Given the magnitudes of the problem, probability will remain zero.
As far as biologists, I work with a couple. They agree that the polypeptide chain would need to assemble. Where "the spark of life" comes in is debatable. So I said, let's just look at the physical structure. What are the probabilities of a nucleic acid molecule self assembling? I did forget one other assumption--namely that energy sources are assumed to be plentiful. This is just to avoid arguments about primeval lightning and geothermal activity, and give evolution every benefit of the doubt.
Cheers!