For one, the arguments are a bit vague at points.
I fully agree with rimv2's observations.
Also:
In 8, the counter-argument is still assuming God is a physical being, which is ruled out in 7. 8a is not valid, were God a physical being: if he had created the 2nd LoT, being a physical entity, he would still be subject to it, therefore, according to 7 (Which is debatable: the 2nd LoT is, bear in mind, -not- a no-excuses law - it merely states that the odds of arbitrary de-enthropizing are very, very slim indeed.), the next step would be 8b - God is a physical being, but immune. Which would make him -slighlty- hypocritical, possibly

- so, in order to avoid that, the counter-argument (still thinking of God as physical) is 8b: God is the ultimate physical improbability.
Following this line of God-physical-improbable, 9a is invalid.
(Now, I'm not sure about other anti-God arguments from this physical side...)
But, the much more plausible construction is to assume that God is -not- a physical being (9b). That is, outside spacetime indeed. I fail to grasp the logic of 10a, though. How and why exactly should spacetime imply the existence of God, and how and why exactly should, because of that, God be contingent on spacetime? Even if we accept the antecedent (spacetime -> God), implication is just a one-way relationship. I simply don't see why should [a non-physical] God need/depend on spacetime.
Now, let's assume there's a good and bulletproof answer to this how&why, but 10b is also a bit odd. It is assuming that contingence means creator-creation relationship?
...
Food for thought: isn't the -point- of God that He can't really be proven/disproven, but rather believed in/not believed in? *goes to ponder*