Full Time B.Com

60% or above would be enough for taking B.Com.

Yes, but see for the timings of the college or university matches with your B.Com and Certificate course, check once the time is well balanced.

After completing a B.Com you can enrol in a wide variety of courses, including M.Com CA CS MBA, ICWA, and many others. For further information, go visit https://www.shiksha.com/accounting-commerce/articles/course-options-after-b-com-blogId-12939 the official Shiksha. Com page. The MBA will be easier for you if, on the other hand, you have already read about many of the topics that will be covered in greater depth, such as international business management, finance, human resource management, marketing management, and operations management.

Hi. Go through this link. https://www.shiksha.com/college/kpr-college-of-arts-science-and-research-coimbatore-106185/courses/bcom-bc.

Yes, you can apply for B.Com regular from any University subject to conditions varies form University to university.

The following is the fee for the B.Com regular
B.Com {Hons. }1.63 Lacs (1st Year Fees)10+2 with 60% + Jain Entrance Test.

There will be no problem with your 12th from open schooling. Because open schooling board like NIOS are recognised by MHRD of government of India. So you will not face any problem in your higher studies.

https://www.shiksha.com/university/jamia-millia-islamia-jmi-Delhi-843/admission
Kindly follow the link.

Here is the complete information about the JMI exam, you can follow the link to know all the eligibility criteria
https://www.shiksha.com/university/jamia-millia-islamia-jmi/jamia-millia-islamia-entrance-exam.

No, you can pursue one degree at a time. Or, you can pursue BCA+ MCA dual degree. Good luck.