new I797 start date is future date, visa stamping


My new extended petition is approved and its start date is on 02/04/2016 and current petition is valid till 02/03/2016 and I am travelling to india in december and my visa was expire july/2014 (old employer).

Which petition number i have enter in DS160 and appointment form?

If it is new petition number can I travel back to US in 1st jan, 2016. Some where i have read that cannot travel 10 before the petition date(02/04/2016).

Please help me out.