<p>The SE team tracks a lot of statistics like these.  You can find some of these statistics on the <a href="https://stackexchange.com/sites#science-questions">SE sites page</a>.  Specific pieces of information are also computable with specialized queries in the <a href="https://data.stackexchange.com/" rel="nofollow noreferrer">SE data explorer</a>, although someone either needs to have already written the query or you need a bit of SQL sophistication to get them (they do have a quick <a href="https://data.stackexchange.com/help" rel="nofollow noreferrer">tutorial</a>).  As @whuber notes, there are some timeseries that are already prepared for convenience; they are available to moderators and to users with <a href="https://stats.stackexchange.com/help/privileges/site-analytics">privileges</a> for reputation >25k.  </p>
