MBA/PGDM

You can do PGDM as it is an equivalent to MBA. You can go to Kohinoor Business School or IBS college, they arrange the loan facility.

Yes, you have to take any of the aptitude tests.

Christ University, Bangalore
Vellore Institute of Management
Loyola College of Management
PSG College of Management
SJIM
Welingkar College of Management
These are some of the good colleges for this CAT percentile.

CAT is mandatory for MBA education. In Amity, an entrance exam conducted by Amity is to be written. So, go for that if you have decided to take admission in Amity University. CAT is a bit difficult as compared to Amity entrance.

Having technical skills and managerial skill will, of course, benefit you. Do a job for one-year after B.Tech and then go for MBA. Experience matters in placement of MBA grads. Digital marketing is one of the booming sectors in the marketing studies. You can own your own firm if you are good in digital marketing.

Yes, you can appear for banking exam along with MBA. MBA from Amity University is a good option. It is one of the reputed private autonomous campuses for MBA education. Doing this from Mumbai is also a good option since it's a metro city with a lot of job opportunities.

Information about the courses is available on the institute website.
Link: www.jbims.edu.

In JBIMS M.Sc finance is a full-time course for 2 years. The institute offers 3 years part-time (MFM / MHRDM / MMM / MIM) courses.
The institute will conduct a separate CET for the part-time program. Criteria is 2+ years of managerial level experience.
Specializations offered are finance, personnel, marketing, and systems.

Yes, you might have done B.Sc which is enough for eligibility. Now, take an entrance exam like CET CMAT, CAT, etc., and apply for colleges to do MBA.

Yes, a perfect option for you as you will be having a base and can do great with both the degrees in IT.