Shall I join an IIM (Kozhikode, and newer ones) as a fresher directly after B.tech or should I take a job that is paying 4.5 LPA and take another go at the CAT/XAT after 2 years for A, B, C,L, FMS & X

Your question has a lot of variables to consider. This answer is unbiased as it can be. You should take a job after B.Tech. if you don’t have a strong resume. MBA is a professional course and welcomes experienced students who are well versed in academic performance, extra-curricular, and leadership/management experience. 

If you lack in these areas my suggestion would be to upgrade your CV with skills and experience and give CAT another shot.

Keep in mind that your salary does not matter. Your achievements, crisis management and leadership skills you acquire while at work are more important. So if you are eyeing a high-end consulting job, take another go at CAT after gaining some more experience.

Some people tend to lose the motivation to prepare for CAT over the years. They can join IIM Kozhikode even as freshers.