H1 visa - question on extension filing and travel/stamping


I converted from L1 to H1 visa in 2012 Oct in COS, and since then have not visited India.
I work in EVC model and plan to travel India in June this year, and have to do stamping there.
I received my I-140 approval recently.
My current petition expires in Sep/30 this year.

1- I want to know if I apply for H1 extension and get three yrs extension before traveling to India, can I get that additional three years in my stamping, or I will only get stamping till Sep this year ?
2- Is there any problem if I file for extension (in premium) before my travel, or I should do it after I return back ?

Thank you in advance for your time !