Science

I think you should go for biomedical engineering.

Of course you can apply for BITSAT.

12th must be all cleared with min 75%.

http://stellamariscollege.edu.in/
Refer this link.

Hello,
Now almost 2 months are left for the IIT JAM 2020 Exam. So, from now you should follow these tips:
Study the most important topics from now. Solve previous year IIT JAM Question Papers. This is the best way to prepare for the exam as this will give you and idea about the pattern and difficulty

Yes you can. But some colleges have restriction.

Yes you can. But some colleges may be restricted. So do some research.

I don't think studying at an open school would do your dreams a great lot good. It would be better to study in a regular college.

There's scope but admission cannot be guaranteed at all the colleges. Do some research.