Onward and onward

I've been mulling over green_knight and accio_aqualung's request for something on plotting multi-volume stories for a few days now. It's not easy, because on this question, I'm working mainly from observation. The closest I've come to writing a multi-volume story myself are 1) the Lyra books, which aren't really a multi-volume story so much as a group of stand-alone novels sharing the same setting and history, and 2) the Enchanted Forest Chronicles, for which I started with Book 4, having no ...