CBSE 12th

For applying in IIM, CAT score matters the most and after clearing the entrance test, you have to prepare well for the personal interview & GD to get admission.
Good luck.

The list of the professional courses you can join after 12th commerce for the same are (please choose them according to your interest area):
Diploma in Web Designing & Development
Diploma in Graphic Designing
Diploma in Game Designing & Development
Diploma in Mobile Application Development
Certificate Course in Web Designing ( HTML5, CSS3, JavaScript and Bootstrap)
PHP Web Development ( Core PHP and Advance PHP)
Android Application Development
Certificate Course in Digital Marketing
C and C+
Java
Web Animation
Motion Graphics
Auto CAD
Digital Fashion/Fashion CAD
Responsive Web Designing

Hi,
Details of some good courses to do after 12th Arts stream
1 B.A. B.A. .
2 B.F.A. B.F.A. .
3 Journalism and Mass Communication. This one is a job oriented and 'in demand' course. .
4 Hotel Management. .
5 B.B.A. .
6 Event Management. .
7 Fashion Design. .
8 Retail and Fashion Merchandise.
Regards.

Yes, you may pursue astrobiology after B.Sc Biology.

Yes, you are. Also, you can get some other additional scholarships.

B.Pharm is the best option in terms of job posting instead of BMLT. Future after the this degree is bright. There are lot of universities which are which are good enough for B.Pharma. Some of them are as follows. For more details, check out the websites the official websites of these universities:
1) Himachal Pradesh University, Shimla, Himachal Pradesh
2) Guru Gobind Singh Indraprastha University, Delhi
3) Lovely Professional University
4) Hemchandracharya North Gujarat University, Gujarat
5) Osmania University, Andhra Pradesh.

Top aeronautical engineering colleges in India:
The ranking is based on engineering ranking 2015 published by The Week.
https://www.google.com/url?sa=t&source=web&rct=j&url=https://www.shiksha.com/b-tech/ranking/top-aeronautical-engineering-colleges-in-india/49-2-0-0-0&ved=0ahUKEwiMprnJpI_cAhWMLo8KHfyfCTYQFggkMAA&usg=AOvVaw1SAozR6JIs-qnPC342tUT9

In engineering, there's a variety of branch you can select. Pursue only in which you are interested and you can handle it easily.
All the best. Go ahead.

It's better to search in online.