Visa stamping on previous approved I797 when extension is in progress.

Hi,I need to travel to India in the month of November 2018 .My current petition is valid till March 2019, And I want to start my I797 extension process in the month of October 2018 (about 6 months before the expiration date).I am looking for answers to below questions:1. Can I go for stamping with current I797 which is valid till March 2019 when extension is in process ?2. My current stamp got expired in July 2018. Can I opt in for drop box facility ?3. Is it okay to go for visa stamping when you have only 3-4 months left on currant I797 ?Thanks in advance!!

May be you go for stamping in mexico first.