Exam

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 l

GRE is necessary for securing admission for competitive courses like mechanical, aeronautical, civil or automobile engineering.
Other than that, it is not mandatory. You need to appear for scholarship tests like IELTS or TOEFL. German language certificate could be an added advantage but not mandatory

There are approximately 400+ colleges. You should try with top fifty colleges. Few among those are Biotech, Taxila, WE School.
Good luck.

There is no technique or statistical model to predict toughness of any entrance examination. You are advised to study well all subjects to achieve your goal.

Only good time is when you are fully prepared. GRE checks you a lot on vocabulary. So, mugging up around 2500 words is the only difficult part. Other than that, GRE exam is quite easy. You can write it whenever you want.