Hi there, @chrismhs ...
A slight variation on @NoahBoswell's suggestion could be to create a hidden page in each of your modules instead of haivng a separate module that contained all your hidden pages that you didn't want students to see. In a module, you can publish just those items you want students to see and also keep one or more items hidden so that they are only accessible to the instructor. That way, you're not having to scroll to a certain area of your "Modules" page just to get to all hidden items.
I'm not sure if you've heard of Cidi Labs, but they have a product called DesignPLUS which really enhances courses with lots of different elements like banners, content blocks, and many other things. As part of that software, they have some elements that can be inserted into course pages that always remain hidden to students. So, within these hidden areas of a page, you could put info just for the instructor...for example, instructions on how to build a page of content .. or how to fill out a templated page. DesignPLUS is a paid add-on from Cidi Labs.
I hope this extra info will be of some help to you. Take care...be well.