Exam

Yes, definitely, you are eligible man.

Don't complicate it for yourself and take it as a Language Test. Improve your English by reading newspapers and watching shows in english without subtitles. Read English articles and try to understand sentence formation. Then you can also attempt mock IELTS papers online and check your weak points.

You can't as NDA. Right now is only for boys. You can apply for graduate entries like CDSE, AFCAT NCC, JAC, UES.

Not for all. Test youeself through online tests to see whether you need guidance. Written exam is fairly easy to crack it is the SSB that frets aspirants. You can opt for short term SSB coaching if you are not confident about it.

The government colleges in India that offer admission through JEE Mains other than IIT and NIT are-
1. IIIT
2. DTU.

No, you need to crack JEE Mains exam to get admission in NIT colleges.

You can register at UPSC website though NDA protal.

Pursue it from DTU. DTU had good faculty for COE and will definitely make you land at you destination.

It depends upon the entry for which you are applying for . Moreover 90% is good score to be eligible for all entries but do check whether the entry contain written exam or not.

Minerva Academy
Balnoi Academy
Major Kalsi Classes
Cornel Dagar Classes, etc. are the best coaching in India.