Thanks for your response. I understand now that category thumbnails is not (yet) a feature of reviewpost.
1. Can you suggest where I can learn how to make this a feature of my site?
2. I am quite confused by the function of following administrative settings, which make it appear that category thumbnails were an intended feature of reviewpost:
| Show Category Options |
Number of columns for thumbnail pages:
Display # of reviews indicator under thumbnails?: