Dear student,

There is no hard and fast rule or any thumb rule that you go to coaching for preparation of CA.
If you think that you can crack the exam with self study then you should definitely go with self study. But the condition is that your Murray di the sthit study in a proper manner or in other words, in a proper guidance. Because there may be a case that you are working lot of hard work and self study but your direction is wrong so, at least the output will be still zero. So, work hard but in right direction or path.

Or you can join coachings for getting a good mentor or guidance and then prepare for CA. So, you can either do self study or do coaching that completely depends on you.
Both of these have pros and cons. So, choose wisely and do what your inner soul says. If you think you can do CA with self study then you will surely succeed.