India

You must sit for IIT-JEE Main/Advanced and clear both the exams and try to get in Indian Institute For Space Science and Technology-Trivandrum. Its one of the known institute for Aerospace and Avionics related courses.

You can refer to the below mentioned link for the list of top MBA B-Schools in NCR:
https://www.shiksha.com/mba/ranking/top-mba-colleges-in-delhi/ncr/2-2-0-10223-0

Please refer to following link for list of top MBA B-Schools in India: https://www.shiksha.com/mba/ranking/top-mba-colleges-in-india/2-2-0-0-0.
All MBA specialisations are equally good for you as an engineer. As per market data majority of engineers opt for Marketing or Finance as MBA specialisation.

Please refer to following link for list of top MBA B-Schools in India: https://www.shiksha.com/mba/ranking/top-mba-colleges-in-india/2-2-0-0-0

NITs do not have lateral entry admission provision for Diploma holders.

Hi,
Australia requires GMAT and IELTS along with work experience in most of the universities. There are few who offer MBA without work experience. For India, you need to take CAT, MAT, XAT, CMAT, etc. for various MBA schools.

IITs are the best followed by NIT-Durgapur/Rourkela/Nagpur.

If you are getting opportunity to serve nation, be proud in going for it.