Re: ‘I also noticed some references to “Nezha disturbing the sea” . . . and recall Yang Zhenduo telling stories about him at seminars. Do you understand how he fits in with the Great Yu and the Monkey King's "Do-as-you-wish, golden-hoop cudgel"?’
I can’t say that I know much about Nezha or how he fits into the scheme of things. I suspect that the Ming novel Journey to the West is the conduit rather than the source for the more popular versions of these mythical and heroic figures, but it is possibly a source for some of the imagery in taiji tradition. (There are famous stage versions of Monkey. I recall that Yang Zhenduo is a big fan of Beijing opera.)
Sun Wukong’s particular specialty/skill in magic was transformation—the ability to transform himself or objects in order to gain a strategic advantage. I recommend Lisa Raphels’ book, Knowing Words: Wisdom and Cunning in the Classical Traditions of China and Greece. She includes some excellent analysis of Journey to the West, among other things. According to some versions of the story, Sun Wukong obtained his cudgel from the Dragon King at the bottom of the sea, where it was a huge pillar. Monkey was able to transform its shape to the “ruyi” cudgel, but also to a small needle that he could place in, or behind, his ear. Coincidentally, the taijiquan movement, “Needle at Sea Bottom” involves reaching down with the right hand, which then moves up near the right temple, or ear. This is probably just a trivial observation, but I kind of like trivia!
The Great Yu is probably a historical figure who has been mythologized to such a degree that it’s difficult to separate fact from myth. Anne Birrell’s book, Chinese Mythology has a good synopsis on Yu the Great. Also, Mark Edward Lewis has a recent book out on flood myths in early China, which likely deals with Yu. He is one of the most comprehensive and meticulous scholars today in the early China field, in my opinion. There are accounts of Yu the Great in the Book of Documents, the Guanzi, the Huainanzi, the Lushi chunqiu, Shan hai jing, Zhuangzi, and Mengzi. There are certainly common themes among these accounts having to do with his hydraulic engineering, flood control, etc. From some cursory reading, I haven’t yet seen any early accounts regarding his placement of the “sea settling needle” into the Eastern Sea, so that may just be a case of the Xi You Ji’s author appropriating Yu into his story line.