Commerce

This is possible through Concurrent admission system. You can do two courses simultaneously , one at regular college and another at Distance / Colloaorative mode. Better do BCA as regular , as it is higly practical oriented course.
All the Best

Yes, you can join for graduation in Economics. Alternatively you can also enroll for BCA / B.Sc CS if you are interested in computers.

Sure, he can. 12th standard is the basic eligibility for many government jobs, for example Cashier / Clerical positions with various government department, Assistant of State Bank and Associates Banks , Soldier - General of Indian Army etc.He need to clear various PSc /UPSC, bank tests to get these jobs.
He can go for MBA at any time after pursuing graduation any stream

You should go for B.Com.

Yes, you can complete, but you have to give all the exams in just one year.

Both are good in terms of position.
Science and Commerce both are different fields. You should opt for that one in which you can perform well.
If you do well in academics in any of stream that will lead to a good output. So, choose according to your own interest.
Best of luck.

You can go for B.Com.

You can go for B.Com.

It gives you good foundation to MBA marketing. Finance and marketing have more scope. Salaries depend upon which college you studied and in which company you are placed
It is a theoretical subject, more comfortable.