<…> 2. Are there any are specific parts of the forum that you don't accumulate activity from by posting? <…>
There are a couple of boards/childboards where posting does not contribute to the Activity toll:
You've previously posted in the Serious Discussion section, and any posts in that section, and it's child boards don't contribute towards post count. <...>
The other questions (1 and 3) I fell have been answered in the above posts thoroughly enough.