IIM Ahmedabad - Indian Institute of Management

Yes, everyone is eligible to do an MBA. IIMs or any other business school doesn't discriminate students based on educational background. On the contrary, they promote diversity and in the process provide some relaxation to students with non traditional backgrounds. In my personal experience, I have seen a lot of doctors, CA, science graduates doing an MBA.

MBA is the best if done from the best colleges.

You need to have scored at least 60% in class 10th, 12th and graduation and should have completed your graduation from any of the Universities incorporated by an act of the central or state legislature in India or other educational
institutions established by an act of Parliament or declared to be deemed as a University under section 3 of UGC Act,
1956, or possess an equivalent qualification recognized by the Ministry of HRD, Government of India.
Fees for IIMs vary from college to college, but it ranges from 18-20 lakhs for two years course.

No you would probably not. The percentage cutoff for class 10th and 12th for IIMA is 60%. However if you secure an all India rank under 100, you might receive calls from few IIMs.

Yes, Mathematics is a necessary subject as CAT has one section dedicated to Mathematics. Also half the courses that are being taught in IIMs are maths based. However being a commerce graduate you are not at all in a disadvantaged position. There are a lot of commerce graduates studying in IIMA. They don't actually cover advanced mathematics like calculus.

You can check out this link: https://www.shiksha.com/mba/ranking/top-mba-colleges-pune/2-0-0-174-0

GMAT is accepted in IIM if you have worked outside India for at least 18 months and during CAT you were not in India. Cutoffs are usually very high, Last year for IIMA it was 770.

You can find your chances here at https://www.shiksha.com/mba/resources/iim-call-predictor