If an attacker has 50% of the hashrate (q = 0.5), then the math is completely off. No amount of confirmations is going to protect you against that.
Well, each additional confirmation buys you more time. It would take years for someone with 51% to undo a transaction with 1000 confirmations.
No. Run the math. Run the sample Poisson code provided in the whitepaper. An increasing number of confirmation only protects Bitcoin for q < 0.5.
For q >= 0.5, no amount of confirmations can protect anything.
Again, it doesn't protect you, it just buys you time, because the attacker has to start that far back in the chain and build a longer chain. But the attacker will succeed (given enough time).