Many authors of agent their own books very successfully. There are several books in print designed to guide an aspiring author through the business side of their craft. I have never known that to happen in the twenty five years I've been working in the publishing world. Editors are always looking for stories to publish. If an editor reads your manuscript and knows it is great, she also knows that you have many more stories inside of you waiting to be born.
Ideas are a dime a dozen, nothing is original.
It's how you treat your idea that counts. My friend is a great artist. Unless you are also a professional illustrator, art accompanying a manuscript may discourage an editor from publishing your story. Editors prefer to pair unknown writers with known illustrators. I strive to entertain, enlighten, and entice readers to return to my books and read them many times.