Add page counts to sections and groups
Allow users to display a page count next to Sections and Section Groups similar outlook. This would let you choose between showing the total count, unread count or both (total / unread).
have do a report or summary as a button
This is not an essential, but could be interesting to track.
Is there a maximum number per section or file?
On mac also, not just on Windows please
Janne Toikander commented
This is an absolute must. In EN I used smart collections to keep track of my "unfinished" stuff. In Onenote I'm forced to do the same with different notebooks and sections. To keep track of which sections still have pages the count in the sidebar section list is really important.