Editor's don't play guessing games. They don't have time. In my synopses, I sometimes list the main characters and offer a very brief verbal sketch about each one, telling what relationship they have to the story. Many times, for extremely complicated stories, I also include a simple time-line to help simplify what pertinent events happened prior to the opening of the story, usually starting with the birthdates for hero and heroine and any main events pertinent to the story. I usually place the time line either directly after the very brief character sketches or at the very end of the synopsis.
Placement depends on how important the information is in understanding the synopsis.
Use present tense. And use dialogue only when doing so will be shorter than explaining what was said and how and why. The whole concept is to be as brief as possible and if using dialogue cuts down on the wordage, use it, though sparingly. Double space unless otherwise told. Proportional fonts are okay for synopses as long as they are easy to read, but I hear standard Courier is still the best choice for the manuscript itself.