B.A

You may choose Arts(includes History, Geography, Political Science
Optional Subjects: Economics, Psychology)

No nothing like that the paper is not that difficult just fill the form and give the paper along with the class 12th and if you don't get into my side then now in for other colleges the many other colleges for B stats is well and you can definitely go in ISI in your Masters.

Yes, I think you are eligible to go for MCA, because the eligibility for MCA is any graduation degree, you should have. So, you can apply for it apart from this also mention your college so that we can give you better results for that is the general eligibility for MCA.

Hi,
Please check the link below:
https://sgtuniversity.ac.in/course-offered/
Since it is a private university I think you will get an admission here at your rank.

Both are good subjects. Economics will help you pursue a career in financial research, equity research, financial journalism whereas Statistics will give you option of pursuing a career in a range of Data Analytics related field which is in demand now a days. You need to decide on your interest areas, and then based on it choose your specialization.

Yes, you are eligible to do BA Psychology with PCB in class 12th.

No, B.A. In international relationship is not offered by Amity University, Kolkata. List of courses offered by this University in B.A. Is here
https://www.shiksha.com/university/amity-university-Kolkata-46908/courses/ba-bc
Hope it helps you well.