B.Com

Hi Shailja,
Here, you didn't confirm for which test you want to apply. So, it is not possible for me to guide you. Well, as you are in B.Sc. Final year and if you want to apply for any entrance test for M.Sc, then, you can apply for the entrance test. There is no age criteria for any of the entrance exam. Hope this solve your problem.
Best of luck!

Yes, you can, if someone in science stream. He or she may do commerce, arts and BBD is good for commerce.

No. You can get admission in first year though. You can only get lateral entry in BE or B.Tech. Your Diploma will be considered equivalent to 12th for B.Com.

There are several courses you can pursue after B.Com. Although some colleges require more than 50% in Graduation. You can try doing certification courses like in photography or journalism or animation etc. Or pursue a Diploma in whatever field you desire. You can pursue M.Com and then pursue Ph.D. later and attempt NET exam to teach as lecturer.

No, it doesn't matter what Bachelor course or stream you have graduated with at all. That's why, a lot of B.Tech and other students attempt these exams. However, Your 10th and 12th marks are taken in account with your CAT score.

CAT is the best exam for Management studies in India. There are also exams like CMAT, XAT, SNAP, etc. All fields are good for MBA, it is only a matter of your interest.

Yes. No questions about it. Regular means you have to be present regularly for class. Most colleges have atleast 75% attendance requirement. So, try not to fall below that or else, you will have to face a lot of trouble at the end of semester.

MBA in India is 2 years and is considered a Masters Degree. In foreign nations however, it can range from 1 year to 3 years. You will have to check each college individually. Also, not all courses are considered a degree. You will again have to confirm that for each college.

After becoming a B.Com graduate, you can seek entry level opportunities in any of the following areas:
Sales
Customer service
Telecalling
Operations
Accounts
Clerical jobs in government or private companies
Admin asssitant
Front office
Sales man in retail showrooms or malls.

Yes, go. You can explore a lot of certificate courses in graphic designing. However, only pursue them if you have keen interest in the said area and have an aptitude for creativity.