I definitely second Jet Prendeville's advice about spending time looking through existing catalogues raisonnés to get a better sense of the different ways the information can be presented, how extensive the entries are (or aren't), the content of the scholarly essays, and the quality of the images. Although it's certainly a niche area of art publishing and there are certain similarities across various artists' catalogues, the sensibility of each publication is usually quite distinct and specific to the artist.

Since extensive research is the backbone of the project, and since the editor – rather than the author – will ultimately be responsible for establishing a style guide, it seems most important at the early stages to focus on establishing a system to capture and store information (bibliographic entries, exhibition titles and dates, measurements, images etc.) in a very consistent and well-documented way, so that it can later be extracted and formatted for publication.

Best wishes,