Colleges in West Bengal

Whether MEM or MIM depends on your aptitude:
If you can relate to manufacturing industry and are good at (your undergraduate specialisation of ) engineering, MEM is the way to go.
MIM deals with Information Management, and needs further specialisation in a certain type of operations or sub-operation

You should target 99+ for IIM's. You might get a call from FMS with 97-98 percentile.

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.

It is highly unlikely to be honest. All the best anyhow.

The admissions are done on the basis of JEE Main rank so to get a rough idea about the college you can get through below link:
https://www.shiksha.com/b-tech/resources/jee-mains-college-predictor.

Well, you can go for the counselling first then wait for your turn. You may not get it at first round but you can get your seat.

In first round it is difficult but in other rounds you can easily get the seat.