CAT

Yes, you have to take the original copies with you for the security reason, but remember to keep them safe till you get back.

Yes, you can start the preparation for CAT. First check out the syllabus and pattern of CAT exam. Start brushing up the concepts of Maths and English (Grammar). You can sit for CAT exam in your pre-final and final years of graduation. Apart from scoring well in CAT. You must need to score well in graduation. Check out the selection criteria of top-20 MBA institutes of India. This will give you a good idea what are the expectations of institutes from MBA aspirants. Best of Luck.

NIRMA institute accepts CAT score. A score around 85-90 percentile is good enough to get into NIRMA. Check the below link for more information on MBA admissions in NIRMA -
https://www.shiksha.com/college/institute-of-management-nirma-university-gota-Ahmedabad-3029.

Nirma University is better than O P Jindal for Marketing. You can apply through CAT. The highest package as per 2015-16 was INR. 16 Lacs average package was INR. 8.10 Lacs and median package was INR. 8 Lacs.

Yes, you can get admission in a good B. School with a good CAT/MAT/XAT score. If you get Minimum 75 percentile in CAT and Minimum 500 composite score in MAT, you can get admission in MBA in a good B. School. Amity University-Haryana is a good option with these eligibility scores; though you will have to crack our GD/PI round for the selection in the university.

A score around 85 percentile is good enough to get a seat in IIM, Jammu. Maintain at least 75 percentile across all the sections. No GD/PI in the selection criteria yet.

It varies course wise for PGDIM it is 65 and for PGDISEM it is also 65 percentile.

Please find the link below for detailed information:
https://www.shiksha.com/engineering/articles/cbse-class-12th-board-toppers-2017-success-mantras-and-future-plans-blogId-14471
https://www.shiksha.com/mba/articles/colleges-accepting-cat-scores-range-80-to-90-percentile-blogId-11981.

Dear Veera, If you prepare and work hard in a focused manner IIM is not a big deal. The only thing is be sure what you want to pursue and never ever get deviated from your goal. If selected work hard and give the best you can to your studies. This is something that will take your future to new heights.
God bless you.

One needs to score more than 98 percentile to get into top IIMs.