Hard pen calligraphy has a strong foundation. What copybook should I practice now if I want to be a calligrapher?

Hard pen calligraphy cannot be brought into brush calligraphy. You can't be a good calligrapher if you use your hard-pen calligraphy habit to write brush strokes.

If you want to be a calligrapher, you should start with a brush. Since your regular script is very powerful, you can choose to start with the Tang script. Yan, all good, Zhao Ti is a bit of a regular script.

If you want to improve your writing skills, you can practice seal script. Taishan stone carving, Yishan stone carving, Yuanan stone tablet, Yuanshang stone tablet and other cliff stone carvings are all good.

Learning calligraphy should start with the ancient method. If you are simple hard-pen calligraphy, then you are not a calligrapher. If you want to be a calligrapher, you must improve your historical literacy and literary literacy, and you can create good works only if you know well, otherwise you are just a simple calligrapher.