what percentile is needed in CAT to be in BIMM ? And do they give importance to 10 2 3

There is no cut off percentage as such. To be eligible to apply for BIMM, you need to appear in one of the entrance exams. But anything above 75%ile should be safe. It is to be noted that only 30% weightage is given to your entrance scores, Rest depends on how you perform in your GD PI. I'll suggest