Arbitrary rating field
I need a field that will allow content editors to enter a rating while editing a node...


You could use Drupal's built in Field API to do this. Given that a node will already be in edit mode while being rated, you wont need any additional add-on modules.



If you use the integer type, calculations should be simple.  You can override the text like this:

 

To add the images next to each item, you could use CSS.  Each element should have the necessary classes to theme them as required.