Engineer

It depends upon your interest.

It is good. You will get better value than others, if you are trained under BSNL.

In which department you want apply for Assistant Engineer.

After the completion of +2, you should know the basics of the aircraft. To know about this, better prefer any aeronautical engineering college which helps you to understand the concepts of aircraft.

Yes, you can pursue Marine Engineering. You can also get lateral entry in most colleges. Try IMU-CET exam, It is India's prestigious Maritime University that provides many courses in Marine Technology and sciences.

M.Tech degree holders should be able to progress a little faster than fresh BE/B.Tech graduates, because the latter have a somewhat higher learning curve. Otherwise, as a researcher at one of the IITs, IISc, TIFR, or ISRO, or post-Ph.D as an academic professor/researcher, there is ample scope for M.Tech graduates.

Yes, there is 60% chances, you can get admissions with this GATE score.

Sure, I am listing some colleges worth low fee:
University of Oxford.
University of Cambridge.
Imperial College London.
ETH Zurich Swiss Federal Institute of Technology Zurich. University College London (UCL.

For that, you can contact the college authorities as they can only let you know the exact date of commencement of the classes, as there may be spot round counselling going for vacant seats. So that's why they could be delaying the classes.

All MBAs can be pursued by ME students. There is no such restriction. It is just a matter of choice.