It is doable but 120 Pages in a sidemenu is way too much. You should consider having your main page as a list for your Menu. That way you can have a list of 4 levels that contain other lists.
I concord with @zouzouek: if you use you main page like a menu, you can permit to your user to turn back via normal header back menu. In a side menu this is not possible or to much complicated.
You have your main categories that open up to show sub-categories. On click of the sub categories u can navigate to a new page that shows your content and has a back button to your main menu.
You only need to design two templates for this:
1. Main Menu: Display List
2. Content page: Takes the topic that was clicked and displays the information about it. Also displays back button to return to main menu.