Disclaimer : Please excuse me for the delayed attempt for these questions
I have attempted "table space usage" questions 1,2 and 3 in sequence, but the answer for question 3 is mentioned in discussion of question 2 :-).
http://www.sqlservercentral.com/Forums/Topic1206403-1328-3.aspx
"In the real world, one would never calculate the data size to the exact page number."