Hi!
I am finding that I am spending so much time downloading and installing one CMS after another, then spending a few hours learning how to do things only to then discover that it is awkward and/or tedious to do what I want.
I feel your pain. Sadly this is just what you always need to do, if you don't have first-hand recommendations. I also hate that task.
So I thought I would just ask the community first.. I imagine that I might get replies like:
That's perfectly fine of course. I was just not sure if you were already using s9y, or if you are not even having access to an installation.
So, my answer is this more like:
Yes, Serendipity can maintain Static pages using the Static page plugin and allows for parent pages and breadcrumb navigation. However you can also easily adapt Serendipity to maintain "Categories" with usual blog entries, which allows more structurized content. You can adapt a template/plugin so that entries are sorted alphabetically or whatever else sorting routine you might need.
However, I cannot deny that serendipity is aimed for what people usually want to use in a blogging environment: Maintain special pages with specific content.
Serendipty is not, and will never be, a user-driven contribution system like a Wiki. For that, serendipitys entry-based architecture is too much pointed at singular entries, not at collaborated entries. If you want that, a Wiki is currently the really only way to go; I know of no system that is equally well in a CMS, blog and Wiki scope.
A User manual with chapters and things like that could be built with Serendipity, but if that is all you want to do, you will only utilize a very little featureset of Serendipity which is not even the "best" part of the system. In that case, I actually more recommend you to go towards Drupal or Typo3, which are both larger systems that aim for structurized content. However, their userinterface is much more ugly, and their techniques are much harder to deploy and use than a serendipity setup.
So it all boils down to, what you personally like more and where you better see to realize your ideas. This sadly is a task, no community can take from your shoulders.
HTH,
Garvin