IIT

Varanasi has many good coaching centers for entrance examination. I will suggest you to join JRS tutorials. You have be determined and focused to clear JEE with a good rank. All the best.

Chances are there but can't say surely. You may wait till spot round counselling. You can also try CSE related Branches like mathematics and computing IT etc.

Yes, you can. But, it depends on the other students of your category. I will suggest you to wait for the spot round or last round. You may get lower branches.

It is quite tough to get it as your JEE Advanced rank is too low but don't worry, just check the closing rank of different IITs by this link:
http://josaa.nic.in/Result2016/result/OpeningClosingRank.aspx

This year onward, you have to score at least 75% in class 12 marks if not then you have to be placed in top 20 percentile of your bored so if you are in top 20 percentile of your board then you are eligible for IIT exam 2018.
Regards.

Quite tough to get IITs but please check the closing rank of different IITs by josaa according to category:
http://josaa.nic.in/Result2016/result/OpeningClosingRank.aspx

Yes, why not. You can but as IITs are most reputed college in India so you have to be highly qualified to get admission here as today results of JEE Advanced exam is declared and hope you got the results and scored enough to get IITs. Please check the closing rank of IITs by JOSAA:
http://josaa.nic.i

Hello Piyush,
Congrats for securing for a good rank in JEE Advance, if you have to choose between the above two options, definitely go for IIT Powai, for the reputation and also you can change branch after you score decent in first year.
All the Best!

You cannot sit for counselling of NITs. Else, you can get admissions on the basis of your JEE score. Find a link below that will help you to find a college suitable for your rank:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor
Hope this helps you.

If you are determined enough to crack JEE or you think that you will crack it the go for it otherwise you should settle with the available options. One year is very important in life. You will realize this later.