B.Tech Mechanics

It is a good option if you have an inclination towards finance field. You can do well in this field even if you belong to engineering background.

Yes, you can become a pilot after completing B.Tech in mechanical. You can go for MBA in aviation management and you will get decent jobs in this field.
Below mentioned are the top colleges for MBA in aviation management:
1. IIMs
2. Xavier Institute of Mangement – Bhubaneswar.
3. SP Jain Institute of Management and Research – Mumbai.
4. UPES – Dehradun.
5. ICFAI University – Mumbai.

Even with a B.Tech, you can put yourself into the military track.

Yes, this is a good choice. NTTF is a good college and in future there is a good chance to get opportunity in your field.

It is an average university with decent placements, for details check link below :
https://www.shiksha.com/university/sathyabama-institute-of-science-and-technology-chennai-23588/reviews

In order to fulfill your dream of becoming an Astronaut, you are advised to pursue M.Tech in aeronautical engineering and obtain the flying license with more than 1000 hours of flying. By the way, the first astronaut of India was a fighter pilot in Indian Air Force. You may have to move to developed countries to fulfill your dream.

Yes, mechanical engineering graduates are eligible to pursue M.Des in product design. Some of the best institutes, where you should seek for admission are:
1. Industrial Design Center (IDC).
2. IIT – Bombay.
3. IDDC.
4. IIT-Delhi.
5. MIT Institute of Design.
6. NID – Ahmedabad.
7. Symbiosis.
8. UPES School of Design Studies and
9. NIT - Rourkela.
All are good and provide good exposure, faculty and placements.

You should pursue Embedded Robotics & Artificial intelligence course that can help you to improve your career opportunity. You can go abroad for the job as the course gives you the opportunity to.