IIM

If you are enrolled in the two-year PGP programme, then you don't receive any stipend. However, if you are enrolled in the FPM programme (equivalent to doctoral programme) then you are entitled to receive stipend. The stipend ranges from 20K to 35K plus accommodation.

There are chances, if you are a non-engineer with a 99+ percentile. It is much more difficult, if you are an engineer as that would require a very high percentile in order to stand at par with other candidates.

You should try for an executive one year program, as you have significant work experience.

Give CAT. And, then if you clear the cut off, you can try for some scholarship from the colleges. They help a lot. And, you may take an education loan too. Because, once you get a job from IIM, repaying isn't difficult.

It's good that you have the desire to go for another post degree equivalent course (PGDM). Yes, you can take CAT or any other entrance exams like CMAT, XAT, etc. To get admission in your desired college while you are pursuing your M.Sc you will have to work smart to cope with your college studies and entrance exams preparation.

I think you can't pursue Computer Science because it is a Science stream course. You can go for CA if you are interested in accounting ormay go for IIM if you are interested in management or business studies.
On the other hand, IAS is most difficult but if you are interested in extensive study and are a seeker of knowledge, you may go for this.
So all of the courses totally depend on your field of interest.
Your percentage is good, so you can be admitted in a reliable course which you want to do.
However, universities have some other criteria, so it varies. All the best.

Sorry Ankush,
It seems you are unaware of the fact that the prestigious Indian Institute of Management offers only PG Degree in Management. No B.Com, no B.Sc degrees are awarded there. Only MBA and PGDM are offered there.
An exception is IPM - Integrated Program in Management by IIM Indore that offers a course after 12th. But for this year, the application process has been closed now.

By using Shiksha's prediction link, you will find that you will get IIMs with this score or not.

CAT is the only exam that gives you admission in Iims Prepare hard for it and make sure your curriculum Percentages should be good and if you have job experience then its a plus side for Iims and side by side prepare for GD/PI.