JEE Main

That depends on your second attempt result. If you score more than cut-off percentile, then you will for sure be able to write advanced. This year the cut-off might lie around 85 percentile for general candidates
Edit: But if you are sure enough then start preparing from now itself.

Yes you will get NIT.

Fill the college from the highest cutoff to at the worst 95 of last year's and preferably I guess you will get CSE in not se reputed college but might get non tech in prime NIT like Warangal so it depends on your opinion bta branch and college and I would say have CSAB councelling do not forget that you might get both from there.

Hello!
Joint Entrance Examination (JEE) is an engineering entrance test conducted for admission to various engineering colleges in India. It has two different examinations 1. JEE Main and 2. JEE Advanced. To appear for JEE Advanced you must qualify for the JEE-Mains. For complete information you can visit this link https://www.shiksha.com/engineering/jee-main-exam. Hope it helps!

There are various engineering colleges across India, which are providing admission without JEE Main exam such colleges are called private engineering colleges like Manipal, SRM, VIT, but you need to qualify entrance test which is conducted by the respective college. These colleges didn't consider about JEE Main exam and rank. They will provide admission based on their entrance test.

This year NTA has removed the cutoff of 75 percent so it is not necessary for you to give the boards again but if you want to improve your percentage than you can definitely go for it.

Hello Naveen, if you are from open catagory then you are not even eligible for admission into NIT or GFTI's. To help you I am attaching below the cutoffs prescribed by NTA last year for eligibility to appear for JEE Advanced and for seeking admission in NIT's etc.
2021 : Cut-off for JEE Advanced in different categories:-
General : 87.8992241
OBC NCL : 68.0234447
SC : 46.8825338
ST : 34.6728999
Gen EWS : 66.2214845
PwD : 0.0096375
I would strongly advise you to appear for second session of JEE Mains to improve your percentile. Best wishes to you.

I want to clear one thing that IITs are allotted on the basis of JEE advance rank not JEE Mains rank and at 86 percentile, he will not be able to grab any NITs.

Sorry to say but at this percentile you will not get any NIT college, you should look forward for the next attempt and try to get better percentile in it.

Its better to write about the Home state name you belongs. However JEE Main percentile between 90-95 is good enough for NITs in the asked category.