CBSE 12th

There are no other exams than SAT. MIT only accepts SAT score globally.

Amity University takes direct admission. So, you don't need to worry about it. You can go direct and take admission in Amity.

Of course, yes. If you are willing to get placed in good software company, then you must secure atleast 75% in 12th board.

Studying abroad isn't dependent on your 12th marks. You will have to pass IELTS or TOEFL to be eligible to apply first. Then your Economic background is checked. These are the basic procedures to study abroad if you are trying directly. There are so many other criteria too. I would suggest add more details like the subject you want, your english skills and family's economic condition.

Which board did you study under? And what college are you seeking admission in?

By the below criteria, then, you can take admission in the college:
Mathematics as one of the subjects at XII Science. Provisional admission will be given if Mathematics is not of the subjects XII Science till the student clears the Mathematics proficiency test.
Also, refer to the link below for more details:
http://www.gnkhalsa.edu.in/admission/degree-college

You'll get admission easily after completing 2nd and 3rd round. Because many of B.Sc students leave the college after confirmation of admission in engineering colleges. So, due to vacant seats, you'll get admission on these seats. So, be positive.

You just do B.Sc and then, do competitive exams or do your post graduation.