Is it enough to thoroughly read Nishit K Sinha CAT Books?

No, it may not. While lot of concepts, exercises, Mock tests and solved previous CAT papers are available in all the Nishit K Sinha CAT preparation books, you may need to assess yourself on realtime testing situation. For that you would need to join some CAT test series, and will need some help to analyse the errors committed in the mock test for further improvement. However, the decision should be taken need based.