Regarding what user are using Cloud, you would have to build your own versions of the default Cumulocity apps.
There you could e.g. follow this guide to include Google Analytics in your app:
This should allow you to track which apps users are using and where they navigate to within the app.
Cumulocity does product experience tracking using Gainsight on trial tenants.
You might want to override the GainsightService to transmit any custom events, that have been implemented, to Google Analytics.
Regarding how many accounts and devices each use, as not all users of your tenants would have access to all of the data you would get false values when implementing this via Googles script tag in the web applications. A custom microservice could provide you the correct data here.
Regarding what applications are being monitored, I did not actually get what you would like to track hereā¦ What is meant with applications in this context?