I129 Petition Validity for the approved H1B Visa

My I129 Petition has been approved and it is valid from 10/01/2012 to 09/30/2013, I have learnt that in H1B Visa one can stay in US for 6 years. With I129 being valid for one 1 year

  1. Whether I will be able to stay for rest of the 5 Years?

  2. Do I need to file extension for I129 Immediately?

  3. What are the chances of I129 extension getting denied?

  4. What if I don’t fly to US until 09/30/2013 then do I need to file the H1B again and get the approval?