Anurag,
You're off to a good start with the first five letters of your name!
Seriously, the best way to become a herpetologist (in Britain, at least) is to start early. If you're 15 and you think you want to do this for a living, you should by now have, or be starting to have, a good idea about the biology, habitats and identification for the various species local to you. Obviously, India has a far greater variety that the dozen native species we have, so get to know about your local 'patch', what species are there, their behaviour etc. Get out and watch them.
As to your questions, if you have a good background from being an interested amateur, the degree in Biotechnology shouldn’t necessarily hold you back. I would say, though, that if you really want to work with herptiles, a degree in zoology or equivalent may be more useful.
Question 2 I’m not sure of. Are you asking whether there are particular pay band relating to what qualifications you have? Maybe, at a higher level research post in a university, as a general ‘field worker’, probably not. I’ve seen jobs in the UK for herptile workers (with charities like Froglife or the Herpetological Conservation Trust) being paid around £18k to £20+k, which isn’t too bad for conservation work in the UK. For India, I have absolutely no idea what the wages would be like.
3 & 4: Yes, but most probably depends on which university you would do the work at.
5: Specialist herpetologists (as far as I know in the UK) either work in a university doing research on conservation or biology; some work as wranglers (I met a guy at the South East Herp Conference the other month who provided the animals for Snakes on a Plane!); some work as toxicologists studying the venom / toxins and creating anti-venins or applying them for medicinal purposes; and then you have the people that work for wildlife charities / organisations, either in a specialist herp role or just as part of their wider duties in conservation. I suppose, you could always become a consultant (and sell your soul to the devil at the same time) ;>) or, work in a zoo or wildlife park.
Probably not too much information on how things work in India I’m afraid, other contributors may have more experience of that than I!
Best of luck,
Dave.