CBSE 12th

First, you have to register and take admission tests like SAT, ACT TOEFL or IELTS and you have to do really well in these tests, if you are particularly aiming for IVY Leagues.
You have to check the university's website, if they require SAT subject test. You can collect your class 9th, 10th, 11th and 12th grades and SOPs and LORs. The university will also look at your achievements and extra-curricular and finally you can apply to universities of your choice.

Yes, it is. Are you looking for merchant navy or Indian navy? If you get selected for Indian Navy, then it will give you a stable job with lots of adventure. It brings in a lot of prestige also.
Merchant navy enables you to earn a lot of money and visit many countries. Having said so a career in navy means staying away from family for long time and being cut off from shores for days. If that suits you, then there are no reasons why you should not opt for it.

Any student can change his stream to humanities after XII board. You are advised to review detailed eligibility criteria of targeted universities where you intend doing graduation degree in humanities.

Hello,
There are too many career options available after completing your 12th studies.
But firstly you have to decide what you actually want to do & become in your life and then decide your graduation course accordingly.
MBBS
B.Sc.
B.Tech/BE
BCA
Best of luck.

75% and above is fine to get into a good engineering college.

You may opt for BBA & MBA as the career option. These courses will have minimal maths in their syllabus.

You need to have a good study habits practice, written practice, hard work, luck and most important regularity in studies, a good environment and support system to score good grades.

Yes, indeed, you are eligible, but try to score above 99 percentile in CAT for old IIMs and 97 percentile for new IIMs.

You can go for engineering, architecture or interior design.