Having written a veritable essay on the section IV episodes, I have only two very brief comments on these:
1. I had forgotten quite how much VRT tips his hand here. It's amazing, in retrospect, that anyone could doubt that it was (at the very least) not really Marsch writing the prison diary. (But people did! In Pamela Sargent's afterward to the Ace edition, she talks about it as ambiguous and (IMS) undecidable. I hope that Wolfe didn't see the text before it was printed; otherwise it seems rather unkind to someone who is doing you a favor (writing an afterward for your book) to let them go into print with such an error. I know that Wolfe was strict about not spoiling his own mysteries; but surely one ought to stop this side of letting a friend embarass themselves on your behalf.)
2. Your interpretation of the section on the evolution of women — the way it expresses Marsch's impoverished experience, both specifically with women romantically and with people in general — strikes me as brilliant. I have always found that section a bit bizarre & out of place; you nailed it. It's precisely this that is the great strength of your slow method: most interpretations of the book stay at a higher level, and don't touch on all these details; the time you spend on each section allows (and forces) you to examine pretty much all of them. It's a delight.