Thanks Slickremix, much appreciated.
Ad 1.3.) So does this mean it is part of the page itself, not a widget or sidebar? Is there an option to have the menu in a widget/sidebar, so you do not waste all the space below it as whitespace?
ad 2.1) This will create a problem if you have 2 subjects with a similar chapter, won't it?
For example, if you have 2 subjects, doc-it1 & doc-it2, and both have a 'introduction' page, then the URL will be the same?
It is not a strange scenario to have introductions, requirements, conclusions etc in several different docs (reviews, books etc)? So it would be better to have the subject in the URL as in the levels above?