CBSE 12th

Join Diploma in civil and do B.Tech further, you'll be the master of your field.
All the best.

Yes, in fact, you are eligible to seek admission directly in the second year of B.Com.

For Diploma, you need to complete class 10th and qualify an entrance exam. After completing Diploma, you can do BBA.

For your query, let me tell you that you only need to clear a state level entrance exam for Diploma in which you will get a college based on your rank, but I would suggest you that Diploma is to be done after class 10th, now if you go for Diploma, you'll give your 3 years there and then do B.Tech of four years, so instead of this after 12th, you can directly for B.Tech of 4 years, you would save 2 years.

Yes, you can easily get some top NITs and IIITs but I'll prefer you opt for IITs as the name tag of IIT is better than a good NIT also every IIT pack of every branch is good.

No, you are not eligible to appear for the Advanced paper as you haven't scored 75%.

See, if you clear those exams then you can easily appear for the paper but before that appearing for the paper is of no use.

I would say both are different streams. You should first clear your thoughts regarding both the things. If your communication skills are good enough, then you can go for Mass Communication.

As per my opinion and my knowledge, if you want to have a good career in digital marketing, then you must have to choose this subject marketing as a main subject in your graduation. And, most have a good knowledge of Economics. After this, you can go for MBA marketing, and can have a very good score for your future.

As per my knowledge and my opinion, for having a good career in digital marketing, you must have a good knowledge of accounts business and economics subjects. Especially the economics, so after class 12th, as per me you should go for economics honors and have a good study and detailed version of everything related to digital marketing and can have a good better future scope.