Do you need coaching for GMAT or one can excel it with self study for admission in India (ISB Hyderabad and other top colleges)?

I do agree that coaching makes the preparation journey a whole lot easier and smooth. It's a necessity in case you come from a non-Engineering or non-Mathematics background. Moreover the GMAT exam is all about the strategic approach at which the coaching institutes excel at. Their easy yet effective teaching methodology saves your time and reduces your stress considerably.

One of my friends with a non-engineering/non-mathematics background got offers from 3 International B Schools. However he was prepared for GMAT only after his office hours and yet got the offers. Still he claims that the stress and time invested would have been considerably less had he joined a coaching Institute.

Since you are targeting the top B Schools let me tell you that GMAT is just a stepping stone. Your application is a much more impactful criteria as it comprises your career and MBA essays.

Whatever route you choose, remember persistence is the only way you will get through.