A border should definitely be around it. When I did seasonal boards for my class, I did age appropriate, with many colors, and I did the "Main Topic" in larger letters, and the "sub topics" in smaller letters. Also, try to have it spaced equally on sides as well as top to bottom. You can purchase the various size lettering from any parent/teacher store, office depot, or even staples. I also used "colored butcher paper" (also sold in those stores) of one color, and the letters in a different color, with the border in a third color.
it depends on what type of a bulletin board if it is a bulletin board in a school i believe it should be very attractive it should have a bright and dark background if it is in a office it should be quite formal and very neat
One of the important factors to consider is the type of writing. The writing that normally goes on a bulletin board is single spaced. Another factor to consider is the grade of the students in the classroom where you want to structure your board.