IIM

That is not true. However if you graduation percentage in engineering is 78 or 75, you are seriously disadvantaged and would need to do really well in CAT to compensate for that.

Fees of IIM is same irrespective of which major you choose. Also first year course curriculum is same for all and it is only in second year that you can choose HRM subjects. Having said that the fee of different IIMs are different. Fee of IIMA is around Rs.18 Lakhs for two years for IIMB it is close to Rs.20 Lakhs.

Eligibility criteria for CAT is graduation degree. You are eligible for IIM even with a drop year provided you have graduation degree from recognised universty.

You have to first score 50% or above in your degree. And if you want to go into IIMs, have to score above 95percentile in CAT.

Work hard in 12 get good marks, get some good colleges and complete your graduation with approx 55%. Appear for CAT that is Common Aptitude Test- score above 90% in it after that you can apply to IIM, then go clear GDPI,
so good command in English as well as you subject stream is must. You must be good in maths and reasoning.Update your self with general awareness.

For IIM, one needs to take CAT exam first and then series of interviews.

Please refer to following link for requested information: https://www.shiksha.com/mba/ranking/top-mba-colleges-india/2-2-0-0-0

No, It will not create any difficulty in any way. The only requirement for selection in IIM is that you should have completed your graduation with 60% marks. As long as you meet this criteria and get sufficient CAT percentile, you should be good.

There is no fixed answer to this. However you are seriously disadvantaged in terms of your percentages. To make up for that you will have to score really well in CAT. In my personal experience you will need at least 99.7 - 99.8 percentile overall. However the criteria to compute composite score changes every year and also the scoring depends on the incoming batch. But in general with 99.7-99.8 percentile you should get more than one call from IIMs.