Currently, you are able to use the properties 'Number of Sales Activities' and 'Marketing Emails Delivered' to see how many Activities have occurred 'All Time'.
Unfortunately, you are not able to see this on a Weekly, Monthly, Annual or Avergaed basis because Hubspot does not allow you to report on the specific time stamp that a given activity occurred. They only time stamp the Last Activity Date.
I'd like to be able to see how many Sales/Marketing activities occur on average each month and whether that rate is increasing or decreasing across our organization.