JEE Main

To appear in JEE 2017, you need to have minimum 75% in class 12th or should be in the top 20% percentile of your state board.

If you are from Delhi, a score above 180 is sufficient.

First of all, you must know the syllabus of JEE Mains and yes you can crack it, but cracking is not enough. Good marks are necessary for getting admission in NITs.

You need to know that, in an engineering college you have to study in English, so you have to prepare in English with NCERT books.

Manav Rachna, YMCA, Lingayas and B. S. Anagpuria are some of the old and reputed colleges for CSE through JEE exams.

There can be two choices -
If you have scored a good percentage in 12th board exams then you can prepare for JEE Mains by yourself. For this, you can also refer to the study material of ALLEN, RESONANCE or VIBRANT coaching institute. In this case, you can complete your first year of polytechnic also.
The second one is, if you have not secured good percentage in 12th boards then refer to a good coaching institute and try to score good marks in JEE Mains.

Sorry, you can't do it as it requires 10+2 but you can apply for lateral entry in best college like MIT or government college without doing JEE Mains in B.Tech. it's an easier way but you can not appear for IIT.

Yes, its good to take a chance. If you clear your JEE exam then there will be no problem to get the admission. If you couldn't qualify then you will have another option without any loss.

It is IAS because it has more syllabus.

In boards exam 60%+ is better. For CSE in Jadavpur, this year cut off was about 286 rank. In short, you need to get 120-150 out of 200 marks in WBJEE.