CBSE 12th

You need to enter class 12th marks for the radio application.

B.Ed from DU, Jamia, IPU, UPTech, or any college recognized by N.C.T.E. is equally valuable because to get appointed as a teacher after B.Ed, everyone will have to qualify CTET then you have to crack DSSSB, KVS, State (PRT, TGT or PGT).
Undoubtedly, taking admission in good B.Ed college will help you in further competitions, nothing more.
But if you can do study-self then only a degree of B.Ed recognized from N.C.T.E. is sufficient.

You can give CEED, UCEED, NATA, NIFT, NID for colleges offering interior designing course.

It's your choice. If you are good in subjects practically, then you can approach for B.Tech. But, if you have interest in theoretical part of subjects, then you should seek for B.Sc, and the selection of stream should be such that your goal should also be achieved by that. So, all of it is your choice. And, the colleges suitable for the stream can be found on official website of shiksha.com through google.

Hello Pushpendra,
Yes, unlike NEET for medical aspirants, engineering aspirants need to apply for very many entrance exams. Firstly, entrance exam of their own states, entrance exams of almost each & Every deemed university, You too will have to follow above routine.

From IIM A, most probably, yes. IIM Bangalore can be tricky. Depending on your work ex. (I wouldn't count on IIMB) also there is a 80% cutoff for 10th and 12th marks, if I am not wrong.

Please use Shiksha Call Predictor, it would give you a better idea. Try and score the highest, I don't think you would want to score a 99.1 percentile instead of 99.9 percentile just because it is only as much as you need. I hope you get my point.