Hi Susan.  As a long-time interpretive exhibits writer and editor, I highly recommend the National Park Service's Editorial Style Guide as a good place to start.  It was produced by the NPS Harpers Ferry Center, which handles interpretive services (plans, exhibits, waysides, interpretive media, etc) for NPS sites nationwide, so it covers a lot of ground.  Find it at  http://www.nps.gov/hfc/pdf/hfcstyleguide_july2013.pdf.  The NPS/HFC site also has excellent info on readability and accessibility issues for print; see http://www.nps.gov/hfc/accessibility.

Beyond that, the first thing to do is pick your basic style among the three main copyediting styles used in the U.S.:  Chicago, AP, or APA.  Then zero in on the unique things in your institution that need specific rules.  Of course we editor types can debate the nuances of these for days... feel free to respond/argue!
regards,
Faye Goolrick
Certified Interpretive Planner
Atlanta, GA 

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