The jump from building a high-speed neuron, to building a cortex out of them, to building my cortex out of them, to instantiating my mind in them, elides over quite a few interesting problems

I'm sorry, I should have made that part more clear. I just wrote it using "you" in the sense of what would you do? Looking at the situation from the perspective of the AI.

I didn't mean that it actually was some neural simulation of your brain - it's a de novo AI.

I conclude that your estimates are missing enough important terms to be completely disconnected from likely results.

Yes, for brevity I had to simplify greatly. A full analysis would be paper-length. I do think this is the most likely scenario to AGI in rough outline, even if it's not super likely in particular.

Now what? I haven't mastered cognitive science; at best, I have caught up on the state of cognitive science as of the early 21st century

Yes, I wasn't assuming much novel research, more just insight based on current knowledge, lots of intelligence, motivation, and an eternity of time.

Put me in an empty dark room without companionship for a thousand years, and I have no idea what I would do,

Perhaps writing it from the subjective viewpoint was a bad idea. However, there is almost certainly some mind that would and could do this.