CBSE 12th

If you have qualified JEE Mains then there are good colleges like Nirma Institute of Technology and Dhirubhai Ambani Institute of Technology. These are the best colleges for which you have to fill up the online form for counselling. You will be shortlisted on the basis of your 12th and JEE Mains marks.

No you are not eligible for the B.Tech. PCM subjects are included in the syllabus of B.Tech also but biology is the main subject for B.Tech but you can get admission in engineering.

It's your choice if you are okay with it. After the completion of Diploma you will have the option to continue studies for Bachelors or you can go for a job.

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.