JEE

Yes, Neotech Institute of Technology, Vadodara accepts JEE Main scores for admission to BTech courses. To be eligible candidates must pass a Class 12 from a recognised board. Candidates must apply and appear for the JEE Main exam and score good aggregate.

IIT Madras BSc admission is entrance-based as the institute primarily accepts the rank and scores of the JEE Main examination for admission to its full-time BSc programme. However, if candidates wish to apply for the integrated BS plus MS programme, then they can apply for admission through the scores of the IISER Aptitude Test. Therefore, you can join the BSc course at IIT Madras without giving the JEE.   

Scoring 85 in JEE Mains and securing admission in NIT colleges is little challenging. Candidates can select other colleges like state engineering colleges, private engineering colleges, less competitive NIT's and IIT's colleges, etc. 

With an OBC rank of 36000 in JEE Mains, I can give you a general idea to predict colleges based on previous trends:-

I) NITs with lower rank: you may have a chance in NIT Mizoram, NIT Nagaland, NIT Sikkim, NIT Arunachal Pradesh.

II)It might be difficult to get admission in Popular IIITs

III) Government Funded Technical Institutions- you can aim for various GFITs across the country like Assam University - Silchar, Gurukula Kangri Vishwavidyalaya - Haridwar, Institute of Infrastructure, Technology, Research and Management (IITRAM) -Ahmedabad.

There is an less chance to get the government college because your rank is more and the cut off of government college is lesser than you rank.But there is an 50 percent of chance to get a seat in government college.But in government colleges there is no management facilities to join directly.civil engineering is ever green course which most of the students do.but my suggestion course is CSE in government college.Although the civil branch is also very good in government college we can get government jobs.

No, with 82 percentile you are not getting admission in BIT Sindri, you have to score upto 87 with OBC NCL for lower branches

Once you appeared for 12th you will not have any chance to appear for 12th again and it is not possible 

You can appear for the new Mains 2 to 3 times after 12th if you qualify in JEE Mains then only you can able to attempt the JEE advanced 

I hope this answe is clear 

I would rather suggest to go for you next attempt because with CRL 5,00,000 in JEE Mains you would not be able to get CSE in any NIT or iiit. You can go for private college or counseling of other private organizations.

Getting an good government or private college for cseis too difficult

Being an SC category student, one gets a lot of benefits such as low cutoff and reservations for seats in IITs, NITs, and other colleges but one does not get completely free education. Although you can apply for various government as well as private scholarships available which help you financially. You can see an average fee for a general category student costs around INR 9 L while that for SC it comes down to around INR 1.5 L