There are lots of options for ways to do this within Armadillo. If you are really ambiguous about the number of lessons within each module then you might want to consider “hacking” the blog structure. After all a blog is simply a very nice way to organize lots of things: you don’t actually have to create a generic blog in terms of content.
… so for example let’s say you create 10 lessons for Module 1 and 15 lessons for Module 2. No real problem if you hack the blog structure. Simply give each relevant post a category of, e.g., Module 1. I suppose you could also tag by specific lesson (e.g. lesson 1, lesson 2) but mainly if you create, or date, them in chronological order then the lessons will present themselves as intended.
… the key here is not to use the regular navigation. Create special links to go to, e.g., Module 1. Specifically the link will then go to all the posts with the category of Module 1 ordered as you wanted by the chronology you used. This way you create a really flexible system. There’s no need to show categories, archives, and that stuff in a sidebar as they are irrelevant in this example.
At any rate, it’s an idea to consider.
Get the Disqus plugin and it’s super easy to add Disqus commenting to blog pages or regular pages. You’ll need the Blab plugin if you want all your users to have icons/avatars show up.