JEE Main

Yes, you are eligible for JEE mains, but not for JEE advance.

If you have 55% in class 12th, then you are eligible, but if you want NIT or to qualify for IIT, you have to score at least 75% in class 12th.

Hello,
Almost all of these entrance exams are conducted with aim of testing student's ability of logical thinking and knowledge of fundamentals of science. I would therefore advise you to stick to brushing up your basics. Besides, you will have to learn to answer in stipulated time. There are practice papers available, you can try these. But, get answers vetted by your professors.
Best of luck.

Yes, if have science stream with PCM.

No, to clear its cutoff you have to score more than or at least 75% in class 12th.

You can also give the exam when you are appearing in 12th. It is not compulsory to clear before JEE exams. But, after JEE, when you want to take admission then JEE marks and your 12th percentage will be seen.

Physics, chemistry, and maths are required for the joint entrance examination.

Every engineering stream now a days have at least one programming language. So, you can't run away from it. I think you don't need to fear about programming language. It is easy than other subject. You first decide whether which branch you more interested and don't think about other thing.
Best of luck.

Hello,
Those students who have passed their class 12th in the year of 2015 or 2016 are eligible to appear for JEE mains 2017. As you have passed your class 12th in the year of 2012, I am afraid you are not eligible.

No, not yet. Class 11th exam is conducted by the school, not by the board.