The default when you join is 10 points and yes you can see what you have gotten positive/negative rep for in your CP as well as which thread it refers to and comment made to justify the rep +/-

As for what happens if it gets too low, I really have no idea.

BTW people don't use it much here I think, maybe because other users can't see number of points. I have a lousy 14 rep with all my brilliant threads and posts