Any viewer that is not logged in.
I’m not sure I understand your question. If someone responds to a topic via email it creates a post which is counted in the same way as other posts on the dashboard.
Not necessarily. A user might click through to a page and then continue to read (i.e. 1 click, more than one pageview). A ‘pageview’ isn’t the same as reading ‘one page’. Here is more info on how we measure pageviews.