The right logo tells both customers and potential customers a lot about the practice instantly, without much conscious thought on their part. Just as the five-year-old knows that sign means delicious food is near, you want your medical logo design to symbolize what your practice is about.
In the American English, bracket usually refers specifically to the square or box type. In British English, bracket normally refers to the round type, which is called a parenthesis mark in American usage. Parentheses are the curved brackets ( ).
Yes, because a square is just a rhombus where the angles are all right angles. It is more common to call this shape a rhombus, but some people call it a rhomb or even a diamond. The plural is rhombi or rhombuses, and, rarely, rhombbi or rhombbuses (with a double b).