Post hoc probability calculations like these are a Sisyphean task. There are infinite variables to consider, most can’t be properly measured, even ballparked.
On (1), pandemics are arguably more likely to originate in large cities because population density facilitates spread, large wildlife markets are more likely, and they serve as major travel hubs. I’m confused why the denominator is China’s population for (1) but all the world’s BSL-4 labs in (3). I don’t understand the calculation for (2)… that seems the opposite of “fairly easy to get a ballpark figure for.” Ditto for (4).
I’m highly skeptical that it’s even possible to create omnicidal machines. Can you point empirically to a single omnicidal machine that’s been created? What specifically would an OAL-4 machine look like? Whatever it is, just don’t do that. To the extent you do develop anything OAL-4, we should be fine so long as certain safeguards are in place and you encourage others not to develop the same machines. Godspeed.