B.Com

You should have minimum of 50% to 55% in your Bachelors and need to qualify any entrance test ( such as CAT / MAT/ XAT/ NMAT/ CMAT/ GMAT/ NEST ). You can do MBA in any specializations of your interest.

Yes, if you complete graduation with minimum 50% and clear the entrance exam too, you'll be eligible to seek admission in MBA.

https://www.shiksha.com/it-software/course/master-of-computer-application-gujarat-university-navrangpura-ahmedabad-120871
Check out this link, and if the university mentions no specific UG requirements, then you are eligible

Yes, you can appear for the same.

Yes. CDS needs graduation. Hence you are eligible.

B.Com is degree course and CA is professional course. You can pursue both simultaneously as you wish to do. For B.Com you can apply in university or college and for CA you can apply in specific institute. For further details you can check it on site.

Yes, Rabindranath Tagore University provides BA and B.Com. But, I am not sure about the Open Mode but if you have any special condition like you are doing a job or any other reason, then you should contact the college management about this.

There are plenty of courses abroad after B.Com as you wish to do Masters in finance. You can pursue the same and your chances are good.

You can only reappear for the exams again. No other option is left.