Maharashtra

Yes, if you are studying BMS from a good university in Mumbai then it definitely holds value and while doing your BMS also do online courses so that you can increase your skill set.

You would not be able to change your college and stream after admission, it is the drawback of TFWS in Maharashtra for engineering. For more details, check this link:
http://www.dtemaharashtra.gov.in/index.html

Popular design institutions you should apply to this year:
1. Istituto Marangoni, Mumbai
2. International College of Fashion, New Delhi
3. DSK Global, Pune
4. Indian Institute of Gems and Jewellery
5. Gemmological Institute of India, Mumbai
For more details about the college -
https://www.shiksha.com/design/fashion-design/articles/top-5-jewellery-design-colleges-in-india-blogId-11409

Please use the college predictor tool by Shiksha. It will help you to predict the college according to your rank/percentile:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

Please use the college predictor tool by Shiksha. It will help you to predict the college according to your rank/percentile:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor

M.A. In advertising and entertainment is really a very nice and interesting course. Here is the syllabus:
Semester 1:
Management- Film
Management- Animation, VFX and Gaming
Management- Events and Live Media
Overview- Broadcast Media
Radio Overview, Production and Business
Semester 2:
Electives (Provided by University)
Semester 3:
Consumer Behavior
Management-Film
Media Planning and Buying
Semester 4:
Electives (Provided by University)
Another thing is, this course is provided by SK Somaiya College, not KJ Somaiya, so here is your course structure, read it and then choose wisely.

MITCON, Pune has decent faculty and placement statistics. Think in terms of what you are looking for in that institute to learn. Do not just go blindly go for any institute. Do some research, find the area which you want to specialize in, etc.