NIT

I don't know about the reservations, but for admission in a good NIT, you don't have to wait for the JEE Advanced score, you can get admission to the college by getting at least 250 marks in the JEE Mains exam.

No, you can't as you know you have failed in chemistry. You'll not get admission in any NIT or any B.Tech college.

180+ will be required for NIT Bhopal.

200+ marks will BE require for JEE main to get admission in NITs.

Rank near to 1500 in general-PWD category can get you a seat in NITs for OBC and SC/ST PWD category marks required are even slightly lesser.
All the best.

Almost, all the colleges including the private one's consider JEE Mains marks for admission. The cut-off generally varies from college to college and also on the basis of that year's JEE cut-off.
Some colleges also offer direct admission on the basis of class 12th marks.

Eligibility criteria:
IIT JAM 2018 Subject-wise cut-off is mentioned below. Please check, if you made the cut from the marks mentioned below. In Physics, qualifying marks for general category are 19.51 while for SC/ ST/ PWD, it is 9.76. For Physics Paper/
In Chemistry, qualifying marks for General Category students are 14.79 and 7.39 for SC/ST/PWD. For Chemistry Paper of IIT JAM 2018. In Mathematics, qualifying marks for General Category are 23.35 and 11.68 for SC/ST/PWD. Based on IIT JAM Result 2018, candidates will be admitted to institutes if they fall in above eligibility then you are eligible.
All the best.

Not all the NITs are better than VIT.
The starting top 6-7 NIT are definitely better than VIT but if you get to choose between rest of the NITs and VIT choose VIT. Make sure you choose VIT, Vellore and not any other if you also want to enjoy the college life because the placement and all are same for each branch but the campus life you have in Vellore can't be compared to any other campus.
Coming to get a good score, just keep your basics clear the paper for VITEEE is easier than Mains.

Class 12th Score:
1-Language,
2-Physics,
3-Mathematics,
4-Any one of (Chemistry, Biology, Biotechnology, Technical Vocational Subject),
5-Any other subject. At least 45% marks (40 % in case of candidate belonging to reserved category) in each of the subjects. Regards.

Please specify in which NIT you wish to apply and also which branch of M.Sc. you want to apply?