CBSE

Hello Aditya,
Yes, CBSE will be conducting re-exams of economics (class 12th) tomorrow.
https://timesofindia.indiatimes.com/home/education/news/cbse-class-12-economics-paper-2018-important-tips-and-sample-paper/articleshow/63890155.cms

Hello, I think you may get admission but first check through Shiksha JEE College predictor tool. Link: https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor.

Practice, practice and practice. There is no hard and fast rule, you need to know your weakness and strengths. Practice with previous year papers and improve time management. Make a routine and follow it. Revise regularly. Don't forget to take rest, eat good food and take good sleep besides studying.

There are less hopes of getting CSE if you are from general category. All the best!!

No, it is not necessary to be a CBSE student. If you take coaching for IIT from any good coaching institute, you can crack it.

Yes, you can definitely get CSE in SASTRA, Thanjavur. Best of luck for your future and if any query feel free to ask.

Yes, you should. Do your best there and then wait for what happens next and don't think about admission stuff now. Study hard for now and do that part when all your exams are done.
All the best.

Ask the relevant authorities before taking any decision. I am sure you can apply for the same.
Best regards.

If you had given Mains, then surely you are interested in engineering and in those marks, you can also get some good colleges or you can look up for advance.
Regards.