How to bulk create an extra node for each user
Shouldn't be too difficult if you're ok with writing a custom module, I can't think of any other way to iterate through your user base.


Create the node type for storing your statistics with:


Title (compulsory, unfortunately.  consider using Automatic Nodetitles)
Entity Reference field that references a user
Date field for storing the date
Other field/fields to store your statistics

Write a custom module that does the following things:


Iterate through all of your users
Check to see if the user is active
Queries the database to see how many nodes the user has.
Creates a new node containing the information you wish to store.



See how you go and of course ask more, detailed questions about each step showing what you have tried if you really can't work it out through the documentation and existing questions/answers available here and elsewhere.