CBSE 12th

Hello,
You can check the list of college including NIT and IIITs you can get according to your marks and rank here. Use Shiksha JEE College Predictor:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor?utm_source=cconnect&utm_medium=CR_JEECP&utm_campaign=7489993

You can pursue B.Sc, Diploma or switch to self-financing courses.

You need minimum 60% for reputed colleges. But to compete with the people, it is advisable to get above 80% atleast.

Yes,
Diploma holder can apply for jobs where minimum the eligibility is intermediate. You do not need any special document, you only have to attach your Diploma degree with the application form where you have applied.

Yes, you can pursue BA with computer science with your score.

Hi Madhav!
Yes, you are eligible to apply for NDA exam. The qualification for NDA 2018 is:
1. The age limit for the exam will be 16 -19 years (born after 02 June 1999 and before 01 June 2002 (Both Dates Inclusive)
2. It is a UPSC entry for the aspirants who are appearing or have passed 12th class. Candidates can apply for it from 06 June 2018 02 to July 2018 on upsconline. Nic. In and the exam will be conducted on 9 September 2018.

With this rank in JEE you can apply in NITs. You may get any NIT. If you don't get then you can apply for any good autonomous college. You will definitely get admission there.

For MBA admission lots of business school criteria is 50% and 45% for other category and few MBA college consider 60%. At the time of placement some companies' criteria is 60% in 12th and graduation but some have no criteria. Do not worry and prepare for MBA without any hesitation.

Yes, you can choose B.Pharma for further studies.

Yes, you can join fields like aeronautics, biotechnology, mechatronics, mining, etc. These are some good practical branches in India for engineering.