Hello, first of all, I don't think there is an absolute requirement and regulation on whether to use soft brush or hard brush. I have also read this book by Mr. Zhou. It is worthy of recognition that Mr. Zhou's accomplishments in calligraphy are really high, but I don't think this question is absolute. It depends on personal preferences. Before the Tang Dynasty, there was really no sheep brush. At that time, calligraphers mostly used purple brush, because in ancient times, calligraphers were basically officials, so in the Tang Dynasty. It is the pen made of rabbit hair from Xuancheng, Anhui Province. It was not until the Song Dynasty that the so-called Zihao pen was not as hard as the current Langhao pen, so I suggest that you can choose doubled both brush's brush in the beginner stage, that is, the brush with the sheep's hair and the wolf's hair, because this clock pen is neither too hard nor too soft, because it has been used in the beginner stage. If you use the Yanghao pen, you can't control it at all, because the hardness difference between the two pens is too great. Furthermore, if you are a beginner, you usually start with regular script, and regular script is basically Ou, Yan and Liu. Because Zhao has no real script, it is not suitable for laying a foundation, while Ou, Yan and Liu are from the Tang Dynasty, so it is best to choose a pen with a hardness similar to that of the Zihao pen they used at that time, but the current price of Zihao pen is too high, and I personally think it is not necessary, so doubled both brush pen can be used instead.
However, this question is not absolute. What kind of pen to choose depends on your personal preference. I'm just giving you some personal suggestions here, which may not be so accurate, but I hope you can give me some advice.