Which I-797 receipt number to enter while taking an appointment for H-1B stamping

[good_run]

I have three I-797 Receipts as mentioned below (Latest first)

Receipt 1

This is for the H-1B that is filed this year in May.
Start date: 10/01/2013
End Date: 09/30/2016

Receipt 2

This is for the amendment that we filed last year in July.
Start Date: 10/31/2012
End Date: 09/30/2013

Receipt 3

This is the first H-1B that was filed in 2010.
Start Date: 10/01/2010
End Date: 09/30/2013

I have never gone for stamping yet. I would like to go to India in end of July 2013. I have two questions as below -

1. Which receipt number should be entered while taking an appointment for H-1B stamping?
2. When I get my H-1B stamped will it be valid for only next 2 months (August and September 2013) or it will be valid for next three years (10/01/2013 to 09/30/2016)

Kindly let me know.