I would say you don't need taxonomy or anything else, but ONLY a menu structure.
The menu system is enough to define what is the parent and what is the child, and the order of the children.
The Book module (shipped with core) uses the same strategy, but probably you don't even need that.
Problem 1: How to edit large menus?
- The menu configuration form will get very heavy if all menu items are loaded at once.
- There is no convenient bulk editing. Or is there?
- You may want a workflow that lets you build the hierarchy first, and add the nodes later.
Well, Menu editor does help you with the bulk editing. But it can only handle so many menu items at once. No hard limit, but it will slow down everything - but give it a try! There was a feature request that asked for paging, but this is naturally hard within a tree.
It also helps you to create dummy menu links that can be fleshed out (filled with nodes) later (via me_node_creation submodule).
So you could try this and help me improve this thing..
Problem 2: Display sub-page teasers
You said some of your pages are like containers for sub-pages. You probably want these to show a list of sub-pages.
One way I did this on a client side was to use Menupoly and create a custom MenuTheme that will render every link as a node teaser. Then a block via hook_menupoly to display the submenu of the current page using this MenuTheme. I think I should upload that code in a sandbox!
I am sorry, this stuff is all "needs work", and I would love some help. But I think it can all become pretty cool.