JE19426

I'm pretty sure Timbre is Captain Ico's daughter.

I haven't seen any WoB like that but in Hero of Age Pre chapter monologue (for Chapter 22) it stated " That is part of why he was so mighty compared to other Mistborn—though, admittedly, his ability to mix Feruchemy and Allomancy was what produced many of his most spectacular abilities ". I assumed after read BoM that compounding Nicrosil enhanced his Allomancy.

You're either misremembering the scene or mixing it up. In the scene with the bookstore owner Shallan notes that he'll have his wife read it even if he can read, no mention of it being neccasary for hiim to read. It's also worth remember that the book store owner is a Thaylen and they don't have the same standards as the main Vorin nations.