2, according to the lens (framed painting) content. Personally, I feel that flower-and-bird paintings with rounded corners and narrow borders give people a better feeling. Calligraphy works with few words can have wide edges and sharp corners.
Generally speaking, rounded corners give people a more exquisite feeling, while sharp corners give people a more quaint feeling.
4. The width of the general border should match the proportion of the painting center. The wide border gives a heavy feeling. The narrow border gives a sense of exquisiteness and dexterity.