Each of these characters you may know as well as your protagonist and antagonist. They need to be well-rounded and they need to fill a purpose in the story.

Fiction isn't like real life. In real life we have coincidences and odd encounters, but in fiction it means something. So if you have one character who shows up in one scene, think about reusing them somewhere else instead of having a new unknown character show up.

While that doesn't always work, sometimes it can add depth to the story to bring someone back. These minor characters might be liked or hated by readers, depending on what they do, but they're there for depth of story.

Otherwise we might as well throw the protagonist and antagonist in a room and let them brawl it out.

http://www.writersdigest.com/whats-new/what-is-a-minor-character-understanding-t...

http://www.novel-writing-help.com/minor-characters.html
(Realize in this last link that we may be talking Other Major Characters here instead of minor. This might also be a good time to go through your dramatic personae again and judge who to be the major characters and who is minor.)

Happy Writing!