Engineering Entrance Exam

Actually, there are no. of 1-year courses, and even if you want you can pursue any course and then appear for JEE Mains 2020. But I strongly recommend you to join in any of the colleges at present.

You may get admission in a GFTI or any government engineering college located in Delhi.

It's not possible for you to get admission in any of the government colleges, you have to go with private institutes. To know the list of institutes you are eligible to apply, use the college predictor tool:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

If your results are in terms of GPA, just multiply the GPA you got with 9.5 gives you the percentage and enter that where ever you want.

You are not eligible for admission as you need to have at least 45% in PCM.

No, 75% marks are compulsory to take admission in NIT and no composition is considered now.

Yes, it is compulsory to take this exam for admission to this college.

Yes, you can get a college, but not a good college and you can get private colleges by paying some extra fee.

For JEE Mains, you should first join a coaching (avg. not necessarily popular but teachers should be available there for every question) and regular study is needed, and most importantly you should read your NCERT books first then complete all modules including DDPs given at the coaching institutes.

There is a very good chance for you to get NIT-H.
You can refer the link to know more: https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor
Good luck.