CBSE 12th

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

Clat is for LLB and isn't related to DU. Yes you can apply in DU for UG admissions even if you are from a state board and there is no percentage deduction for it.

Yes you can apply in delhi university though chances for admission are a bit tough for general category.

It depends on category and you should be in top 20 percentile of your category in board exam. It differs every year .

If u a student of Science.lot of opportunities are for you. medical, engineering, polytechnic, ITI, etc. If u a student of arts or combined .hi can also try for ITI or polytechnic. other wise General study line is open for both stream.

You should firstly work on clearing your basics.

Yes, if you can secure good marks in JEE Mains.