You can leave the illustrations and dummy completely off, as publishers like to pick the illustrator, and the illustrator will decide what the characters and scenes will look like. You can include an illustration note if there is something that is not clear in the text, otherwise leave it for the illustrator to imagine how your story looks.
Some writers make a dummy for themselves while writing to see how the words and page turns work, but don't send it in with the text.
Good luck!