When you say "next book", how far into the series are you ? Some of your questions would strike me as at least implicitly answered in book 4, and the series is up to 5 with a promise of really big revelations in 6.

Not particularly freewheeling, I suppose, and certainly not so actiony as the Dresden books, which is a plus from my perspective because I usually find action scenes dull. I would posit that they do indeed do intricate puzzles, though, but in an Asimovian sort of mode where gathering data to figure out how the hell the world works is the biggest part. And urban fantasy recast as Asimovian scientific-mystery for supernatural values of science just totally hits my buttons.