IIM

You will need a thorough preparation and may need the help of a coaching institute for the same. Right now, keep your focus on getting a good score in B.Com then take a break for preparation for CAT / MAT exam.

You can check the below mentioned link:
https://www.shiksha.com/mba/ranking/top-mba-colleges-bangalore/2-0-0-278-0

You can appear for CAT exam and try to score 99 percentile to 100 percentile. Then, do your best in GD and PI. Overall, you have to be the best, if you wish to go to IIM - Ahmedabad.

As better career opportunities and job prospects are concerned, you may consider:
1. M.Com in SRCC - Delhi along with CS.
2. MBA from JIMS.
It also depends on your interest and preference.
All the best.

Yes, it's possible. However, you will mostly get few IIMs like IIM - Jammu, Nagpur, Amritsar, etc. and if you get above 95 percentile, then you can expect a call from better IIMs like Kashipur, Ranchi, etc.
Good luck.

Yes. To some extent. They do give you some extra points if you have some years of work experience. But you need to have atleast 2 years of work experience for that. Anything less than that will be of no use. And anything above 4 years is also of no use.
But again with awesome CAT percentile and good profile you can still get a call for GDPI with no experience.
Good luck.

Yes, you are eligible for the same.

Yes, indeed, you are eligible, but try to score above 99 percentile in CAT for old IIMs and 97 percentile for new IIMs.

If money is a constraint, then FMS is the best solution for this problem. Though loans are easily available in the market on the name of IIMs. However, I do agree with your point that loans can be burdensome on you as well as your parents. Hence, if you are not willing to spend much money into MBA, then FMS is the college for you.

First of all, every college is good. Be it IIM or FMS, every college has its own merits and demerits. Hence, it becomes more of a personal choice on which college to select.
However, according to my personal opinion, if you are interested in marketing then FMS is the college for you and if you finance focused, then concentrate on IIMs, especially IIM Calcutta.