Accounting & Commerce

You should go with CS executive preparation because it can provide you with a managerial position in any reputed company and the need is only of commerce and accounting related subjects, whereas, in CAT there is a lot of competition and topics to be covered are hard.

You should prepare for banking first because you can get a job of an accountant whenever you want. I suggest that you should do sales job instead of accounts because you can get a good salary package and it is easy to get. Please feel free to ask any other question.

As a final year B.Com student, you can seek provisional admission for PG Diploma in banking and finance (1-year full-time degree) or MBA in banking & finance (2-year full-time degree).

No, there is no compulsion.
You have many other options such as CA, ICWA, MBA, etc.

MBA is a natural choice for you. Please, take up the course with additional preparation. You pay interest in soft skills from the beginning, to save your time.