sxyz
1. Do the good (say top 30) B-schools
require credentials verified by a third party at the time of submission of application or they do it on their own?
They expect you to write the truth in your application. Background checks etc. are done at a later stage when applicants are made an offer.
sxyz
2. I did not have a GPA in my college in India. I read in some online forum a few hours earlier that you can convert your scores to GPA online by
WES GPA calculator. But to my dismay,they did not have India in their list! So how can I get an idea of my GPA now? (I really need to know this before starting dreaming big!

)
There are just a handful of schools that will ask you to use the WES or do a conversion (if at all). Most ask for your scores the way they are, and they would require you to upload scans of your undergrad transcripts. So let this not bother you.
sxyz
3. Is it real that the GMAT does not stress on an extensive and outlandish vocabulary unlike GRE? (if it's true then I am more than happy!

)
No. Its much simpler.