IIM Ahmedabad - Indian Institute of Management

You can expect Rs 9.5lacs per annum as fees all inclusive.
http://m.economictimes.com/industry/services/education/fees-in-top-b-schools-to-rise-by-rs-46k-3-2-lakh-depending-on-the-institute/articleshow/51749368.cms

Best thing you can do is to introspect about your life, reason for doing MBA. Make a story about your life's journey and stay updated with the current affairs & build your own opinion on those topics. These will give you a head start for interviews & WAT

Placement is not an issue at IIM-A FABM. People get placed in a matter of hours. Profile ranges from marketing to supply chain management in agribusiness and some FMCG companies.

You have got fantastic score and you are surely eligible. You can also check alternate colleges with similar ranks below:
https://www.shiksha.com/mba/ranking/top-mba-colleges-india-accepting-gmat/2-2-0-0-310

Yes, you can take admission in other courses. The cutoff for HR is higher than others. You can go for marketing, finance, IT or RM.

I believe, basic mathematics is a must for MBA exams and later stage in life as a manager also. I would suggest you to practice and get acquainted with basic mathematics, and then think about doing MBA in IT in any college with decent placements. Without a decent score in exam will refrain you from

Civil engineering won't help you much while doing your MBA. At the same time it won't put you at a disadvantage either. But incase you are inclined towards engineering degree, the closest you get it by choosing Operations specialisation. Good luck!

You sure do. But aim for a higher percentile in the range of 99.6+ for getting a call & converting it .

Very less importance on extra curricular activities, more on work experience,internship, certification and academic qualifications are given at all top B Schools.