Dear,

Salam,

I would like to say that the study of one or more books makes no difference in the preparation of CSS.The thing that matters greatly is only your grasping power.If you are able to catch much more things from one book,and all aspects of the topic that is under your reference if are clear to you,it is enough for you to go only through one book.In case the things are not clear to you then for the clarification of that you may refer to two or more books.
Regards essay,you have need of practice.You write again and again about any topic and check it for errors and further revision.

Best of luck,
Inayatullah Rustamani,
Wahi Pandhi,Dadu,Sindh.