Esslemont really picks up in Return of the Crimson Guard and Stonewielder (2&3.)
1. I think the 'broken' part of Koryk was his viciousness. His objection was that, like us, he didn't see it coming that they had to kill TCG to release him. I trust Fid that it was the only way.
2. Itkovian, while not directly influencing the ending, did team up with Mother Dark to save Black Coral from the Dying God. Which freed Nimander/Spinnock to lead the Andii to the Shore and stop the Liosan from taking Kharkanas and the Hold of Darkness. The Liosan are also loosely allied with the Forkrul Assail iirc. Them winning would have been very very bad for our protagonists at the final battle.
3. No one knows who Ruthan Gudd is. But everyone has a theory.
4. Draconus presumably keeps hunting other Elder Gods, but makes an appearance again in the Esslemont books.
5. I don't remember anything about Bolkando coming back up or the Queen's ensorcelled Segulah being mentioned again. RAFO Esslemont to find out about the pickled ones.
Really glad you enjoyed it! Great final thoughts too, I got chills a couple times just reading your highlights.