Diploma

Yes, in a few colleges entrance exams are conducted and in a few colleges it is based on merit of Bachelors degree.
Few best colleges for the following are:-
Indian Institute of Mass communication (IIMC)
YMCA institute of Media Studies and Information technology
Bhabha institute of Management Sciences
Aligarh Muslim University

Hi,
Yes, there is PG Diploma in music production. Some of the good colleges are:-
Satyajit Ray Film and Television Institute
IGNOU- Indira Gandhi National Open University

Hello Rutuja,
There are plenty of good engineering colleges in these two cities of Maharashtra. With 80% in your Diploma, I am sure you will be able to get admission in your desired college. I am attaching a link that will give you list of top engineering colleges in Maharashtra. You can choose any college from this list.
https://www.shiksha.com/b-tech/ranking/top-engineering-colleges-in-Maharashtra/44-2-114-0-0

It depends on your priority. If your financial condition is not good or you want to get an early job then opt for Diploma otherwise continue with your class 12th.

Yes, it is recognised and approved.

Hi Krishna,
Most employers require automobile designers to earn at least a Bachelors degree in engineering, industrial design, transportation design, or mechanical engineering with an automotive design concentration. Design schools require students to submit portfolios or samples of work during the application process.