CAD/CAM/CAE

Hello Surajit, it's very nice to know your desire to do M.Tech though via online course. How Ava I would not like to recommend that you should follow this path. Firstly because professional courses are not be done online they need to be done in physical mode only. Secondly in many cases such courses have not been accepted by the approving authorities. You should look for doing something else other than M.Tech. Best wishes to you.

NID and CEPT University are the best Interior design colleges in India for pursuing undergraduate courses after the 12th. The diploma Interior design course fee for one year is about Rs 30000/

Yes, you can. Bachelor of Business Administration BBA An undergraduate course is designed to enhance leadership skills, management skills, interpersonal and communication skills. If you are interested in Management related field so this is better option for u. I am sharing you the link below, you can find all the relevant details related to respective Course. Link:-
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/bba-bachelor-of-business-administration-chp&ved=2ahUKEwia_Y3wnJXqAhUkwzgGHVzfBaMQtwIwIXoECAgQAQ&usg=AOvVaw0UFOtPoazkGzO7pQRBnD47
Happy to help
All the best.

In my opinion you should choose between Mathematical sciences and Physical sciences. While the Mathematical sciences is most preferred subject for CSIR UGC NET for PG Engineering aspirants.