By this time your friend should give up on thinking he will be able to study in the USA and instead should consider other English speaking...

You definitely can as long as we are talking about a family petition based I-485 here.

Who fills out form 864,and who fills out form 864a?

The sponsored alien is not required to sign supplement A. Only the household member of a co-sponsor normally is.

What if I do not have a copy of the original I-864 that was sent to NVC?

Should not be a problem at that stage, for the reasons explained by my colleague.

I have submitted my OPT(i-765). Realized that my passport size photo is a bit shorter than 2 inches in height. Will this affect?

Rather than speculate - and ask others to do so as well - wait and see what happens in the next 4-6 weeks. Will know for sure by then.

1. Not at all - you are only the "dependent" spouse derivative. 2. Hard to tell -depends on the response speed - at least 4 weeks. 3. ...

Can I reenter the US after a short cruise to Mexico using B1/B2 visa after my sevis is terminated?

You will likely not be allowed back into the US under the facts you cited, unless with a new visa.

Do I need to maintain the H1B status until Green Card application get approved?

I agree with my colleagues - maintain status at all cost if applying through the F2A category.

N-400 Three months residency requirement

You meet the 3 months prior residency requirement under the facts you cited.

You meant a "date rape" drug? No need to mention/bring up unless specifically asked about it.