Exam

There is no such percentage required for NDA. Just pass in 12th standard is sufficient to apply for NDA Exam. Regards.

Yes, there are chances of you getting it, provided you mark Presidency University as the first preference at the time of option entry.

Yes, of course. You may even get it in the first campus, that is, Ktr campus.

Not being able to clear the SSC for second time in a row means your basics are weak and you will be able to grasp the future learnings, if basics are not clear. I would suggest you to prepare well and clear your SSC exam firstly than think of taking admission to any University or College. Presently

For TUM, GATE score should be high enough. But writing only GATE is not enough, you have to write GRE tougher and trickier than GATE to study abroad.

No, it's not a wise idea. Go for coaching along with your studies. Both have the same syllabus. A proper mock test will help you get a good score along with your studies.

COMEDK 2018 College Predictor
Use your COMEDK 2018 rank to see where you can get admission at the link provided below:
See the courses, colleges & rounds you may crack. The result is based on admissions data of COMEDK 2017. Get resources, insights on colleges & courses:
https://www.shiksha.com/b-tech/r

Yes, you are eligible to take CAT exam.