CBSE 12th

No, you can't pursue Master's degree directly after your PUC / 12th because there is no such way to do so, and you need to pursue a UG before pursuing a Master's degree course.

To repeat your class 12th, you need to write all the exams again so, take supplementary exams for all the 3 subjects.

Yes, with your record, you can go with this university.

There is a criterion for admission as you have to fill the application form and then there will be an English test and a personal interview for the admission process.

There are many courses which you can do after PUC (commerce) like BCA and CA. The most in-demand course is CA and it is also the toughest one, but the decision depends on your interest and what you want to do. I think B.Com is the best option here.

Only those who have completed their graduation successfully can pursue a Master's degree from a particular college. So, you need to first finish your graduation.

Please mention your PUC branch, so that I can suggest you the right course according to your field. So do write a little more detailed question.

Here is a list of best MBA Colleges in Coimbatore:
Amrita School of Business
PSG Institute of Management
Coimbatore Institute of Management and Technology (CIMAT)
Karunya Institute of Technology and Sciences (Deemed to be University)
Jansons School of Business
Sardar Vallabhbhai Patel International School of Textiles & Management
Nehru College of Management
Sri Krishna Institute Of Management
RVS Institute of Management Studies & Research
GRG School of Management Studies.