CAT

You should do it with the final year of your graduation.

You can go for the books of McGraw Hill publications.

TIME is the best option.

With 74% in 12th it would be difficult to get a call from IIM A since it gives much weight-age to academics. According to previous trends, you can still expect a call if you manage a 99.8 percentile or more.

CAT score - 60%, GD- 7.50%, PI- 20%, 10th marks - 5%, 12th marks- 5%. The following breakdown is available in detail in the eligibility section of the application form.

If you score between 96 to 99.5 percentile you have decent chances. Please check detailed cutoff below.
https://www.shiksha.com/mba/course/post-graduate-program-management-indian-institute-management-iim-a/1653

To prepare for CAT exam you need to do some self-preparation and you can also do some classes for good marks in CAT. You require some hard work to score good in CAT.

Admissions will be made on the basis of percentile/score in CAT-2016/GMAT, performance in academic writing test (AWT) and personal interview, academic (10th,12thand Graduation), co-curricular and extra-curricular achievements, and work experience. Start preparing by giving more mock exams.

Yes you can get into IIM Ahmedabad if you score well between 95-99 percentile.
https://www.shiksha.com/mba/course/post-graduate-program-management-indian-institute-management-iim-a/1653

Admission Open for MBA(RM) 2017-19 batch, Two-year full time residential MBA(RM) Programme KIIT School of Rural Management, KIIT University,
For More Information see www.ksrm.ac.in/web