Change of Status from F1 to H1

[Jamshad]

Hi,

I am currently in F1 visa, EAD (STEM extension) valid till Dec 31, 2013.

I travelled to India on March 30,2013 before my H1B application filing(I-129 and Change of status).

My H1b was filed after I left to India in F1 status and the dates on my I-797A notice are:

Receipt date: April 7, 2013.

Approval Notice date: April 17, 2013

I returned back to US on May 14th in F1(EAD).

Questions

1. Will my change of status be valid effective Oct 1, 2013.

(OR)

2. Do I need to go for stamping before Oct 1,2013 to maintain a valid status in the US.

3. I got the I-797A Notice of Action with my old I-94# on it. However, I got a new I -94 when I returned back to US on May 14th. Will that be an issue?

4. My employer forwarded me the I-797A notice and my H1b is issued for 3 years starting Oct 1, 2013. But, the online USCIS case status is still in ACCEPTANCE stage. Not updated yet. Will that be an issue?

Please reply me ASAP as I have few more months to decide on leaving the US to either INDIA/CANADA for stamping.

Thanks.