Computers & IT (Non-Engg)

Sorry, I don't think you're eligible for VIT. They require a candidate to score at least 70% in +2 in order to be eligible. So, you can't pursue BCA from VIT. But there are many other universities which will get you admission. You can try Christ University Bangalore, which is also considered as one of the best universities for BCA candidates.
If you want to learn programming languages which you will be studying in your BCA course then you can check out this app "BCA - Course Programming" which is specially designed and developed for BCA students and is available on Google Play Store. It has programs and assignments of languages like C, C+ and Java with their outputs. You'll be studying these languages in your 3 years of BCA.

It all depends on you. Chemical engineering involves designing reactors for various chemical reactions and it has also a major role in energy production. There are various main fields in chemical engineering.
Petroleum Processing
Pharmaceutical Science
Energy Storage
Energy production
Simulation of various reactions and reactors
If you have interest in any of these things, chemical engineering will be better. Biotechnology involves studies related to living organisms, etc. It involves testing new medicines in animals, gene and DNA studies, etc. Biotech is more of Science rather than engineering. Maths is relatively less in Biotech. Finally, it's based on what you love to do. Pursue what you like rather than finding out which field has better opportunities. I've experience in end-to-end development of a software and I've had the opportunity to handle entire apps from back-end to front-end alone. I used to work for around 12 hours a day during the phases where the pay was too low to survive. Life could be easier in MNCs, but I believe that my experience could pay off at some point of life. I never cared about the name or reputation of the company, but I believe that it gave me some genuine opportunities, which I would have missed if I had chosen some support jobs I was offered in the past.