Plan structure

Hi
I am trying to  add a query progress indicator in postgres.Being a 
novice to the code I need help on few topics.
1.Where can we keep such a progress indicator code ?
2.What is the exact structure of plan returned by the planner ?
3.Does the planner return the estimates calculated while deciding   the 
plan ?
4.If not , then from where can we obtain those estimates ( estimates 
taken to decide the best plan ) ?      I will be very thankful if someone can throw light in these 
issues and provide some related guidance

regards
Anuj