New answers tagged reference-materials
There's a modern copywriting guide for Chinese: 中文文案排版指北 https://github.com/sparanoid/chinese-copywriting-guidelines
Wiktionary lists the vietnamese pronunciations for every chinese character they have info on (at the bottom of every page under the "Vietnamese" heading). Other than that, the Nom Foundation database is good for converting vietnamese words to chu nom by sound, though you'll need to know enough characters to know what you're picking, which you also gave ...
After more googling, I didn't really find any book reference materials, but I did find really good online tools that give me exactly what I wanted: the handy look up tool of the Vietnamese Nôm Preservation Foundation http://www.nomfoundation.org/nom-tools/Nom-Lookup-Tool/Nom-Lookup-Tool the equivalent tool from a site about learning chữ nôm ...
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