Whether to leave two spaces at the beginning depends on personal preference and writing style. Traditionally, there is no need to leave two spaces at the beginning of vertical letters. Generally speaking, we write from right to left, so the beginning of each paragraph should be next to the end of the previous paragraph.
As for whether to divide chapters or not, it also depends on your writing style and content. If you want to make your letter look clearer and easier to read, you can add paragraphs in appropriate places. Segmentation can help readers better understand your content and make letters more attractive. However, if your content is continuous, it is ok to have no segmentation.
In short, the format of vertical calligraphy varies from person to person, and can be decided according to one's own preferences and writing style.