Everyone has different methods and decides according to their own habits. I like memorizing word books, and it's not messy. I think it is helpful to compare the differences between words with similar forms. Actually, either one will do. The purpose is to increase the number of words.
Since there are ready-made listening and reading books, make them. It is better to concentrate on one book than to finish five books carelessly. Besides, there are so many books on the market, which one is better is a matter of opinion.
The answer is the same. Do your best.
5. Either one will do. I use sparks. I suggest you choose between Spark and New Oriental. I am in Zhongguancun Book Building, and the clerk told me that these two stores sell the best. The spark of choice after comparison.
Supplement to the question:
I don't know why you bought so many Wang Changxi. Anyway, as far as I know, it's good to buy New Oriental and Spark in grade four or six. Spark must be bought for English majors. Others like Huayan and Wang Changxi are not as good as in previous years. Just go to any bookstore and ask.
In a word, I think if you have books at hand, you'd better finish reading them first. If you need other books, you can buy them again, otherwise it is really a waste of resources. Remember to do the real questions. Good luck.