I have to admit that the newbie restriction was annoying at first, but it makes sense. You can't just post senseless crap right away. However, for you to get rid of the noob status, you need to post. So the new users just leave useless junk, such as "+1", just to get more activity points.
The number of posts doesn't matter with regard to activity.
Yes, it does. If your post count is less than the activity you would otherwise have, your post count becomes your activity.
You are both wrong. It's min(14*time, posts) so if time spent on the site is less than the number of posts, then it counts the time. Vise versa. Nonetheless, people will post junk, so the newbie feature is pretty awesome.