CAT

Dear Mradul,
Since you must be aware of the fact that CAT is a national level test and GMAT is preferably for abroad studies so difference among both is quite obvious so it would be wrong if we consider preparation of one sufficient for other as well.
Good luck!

A minimum of 6 months is must for getting good percentile.

You need to have a valid management test score(MAT/CAT) unless and until which you can't apply for admission to the desired course.

Placement depends on various factors, it was around 90 - 95 % last time. Yes, there is a mandatory international trip for all students. CAT score is itself sufficient to apply for GD/PI.

Cat tests on English, math, reasoning, gk. Various topics. GMAT tests on the depth of a few topics of math English and reasoning. Cat is not considered abroad but GMAT is accepted in India and abroad. GMAT score is valid for five years

IIM Ahmadabad announce notification for CAT during June and July every year for admission into all IIMs once you apply and appear for CAT if your percentile is something which is required then you will be called for GD and PI and on the basis of overall process, you will be allotted respective IIM (assume you need 98 percentile and above to get admission). Except IIM many other institute Also accept CAT score, shortlist such institute and apply individually.

With 78% in CAT, you can able to get into many government organizations . If you belong to reserved category with perfect sectional cutoffs, you may get IIM calls to . Good luck

You can get full information about CAT exam from Shiksha's MBA entrance exam list.

Dear Aspirant,
Thanks for forwarding your query.
You need to fill an online application form by visiting at www.amity.edu/mumbai and appear for the written test and interview for the upcoming test scheduled in June 2017.
Warm Regards
Amity University Mumbai