CBSE 12th

There is no branch of engineering which is good or bad. Better is the branch in which you have interest because if you will have interest then only you can complete your engineering and can get high paid jobs. So, choose the branch in which you are interested.

For the candidates to qualify for the admission in the IITs/NITs/IIITs and such other CFTIs whose admissions are based on the JEE (Advanced)/JEE(Main) ranks, they should have secured at least 75% marks in the 12thclass examination, or be in the top 20 percentile in the 12th class examination conducted by the respective Boards.

Yes, an employer won't hire anyone in a marketing department unless they have a business degree or at least a graduation. Digital marketing is an extension of marketing and one need to have skills like communication, business acumen, using some tools, etc.

No, because last year's BA (Hons) first cut-off list is 98.20%.
Even if you belong to SC or ST category, the minimum required percentage is 85.

If you are interested in accounts, take admission for B.Com and then enjoy your subject.
But, for this, you must clear your basic of accounting.

12th marks are not included in counselling for NITs but you should have scored the eligible scores in the board exam to get NITs.
The minimum marks to be obtained in board exams are 75%. It is applicable for JEE Advanced also but it is better to score at least 75%.

Choose a path based on your interest, both are pretty good.

Campus placements are mainly based on percentage scored in the current course. School result will not be counted. Also, it depends on the college as what %age placements are provided. Speak to college authorities about this. I would suggest you still appear for the campus placements - might get lucky if selected.