NIT

The admission mainly depends on JEE examination. To get into NITs, good score in JEE Mains is required. To get into IITs, good score in JEE Advanced is required.

No. The order goes like this:
IIT
IIIT
NIT
GFTIs
So, IIIT is better than NIT. But, I suggest you to not choose according to this because it may differ from few respects. So, choose when you are satisfied. Also, if you are getting NIT, then enroll for it whether it is very far away from your home or it is a new NIT.
Best of luck.

You might come across certain difficulties in dropping 2 years as with your age you won't be able to apply to some colleges. You should consider you age as a factor first and if you think you can do well by dropping twice you should go ahead with your plan.
good luck.

It will depend on Category. For General, there will be less marks for NIT.

You should use the Shiksha JEE Mains College Predictor. Link is below:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor?utm_source=connect&utm_medium=CR_JEECP&utm_campaign=6540165.

Hello Adyasha, The admission at NITs is based on JEE Mains score only and not JEE Advanced. So if you have a good score in Mains, then you can get a seat. All the best.

Please mention which NIT you are targeting so that I may be able to populate relevant details regarding eligibility. General eligibility criteria for getting admission in NITs for BE/B.Tech is:
Required criteria based on class 12th / equivalent qualifying examination:
1-Language,
2-Physics,
3-Mathematics,
4-Any one of (chemistry, biology, biotechnology, technical vocational subject), 5-Any other subject.
With at least 45% marks (40 % in case of candidate belonging to reserved category) in each of the subjects.

Please refer to the link provided below for a detailed list of courses offered by NIT, Nagpur and their eligibility criteria and admission process followed for these courses.
https://www.shiksha.com/college/nagpur-institute-of-technology-42631

You can apply for JEE Mains but not for JEE Advanced because your percentage is less than 75%, but JEE Mains 2018 exam got over on 5/4/18.

Depends on your category. If you are from general category, you might not get any NIT with these marks. Prepare for Advance, and do well to create better chances for you.