Plain text (2-3 paragraphs), a couple of accompanying pictures (photo or
simple diagrams/plots) and links for further reading should be enough.
When they are ready, they should contact me [Marco], and the EPO group will work
with the authors to get a final draft. Once the paper is ready to be
released, EPO and WEB committees will work together to prepare the web
page and publish it in ligo.org.
The first paragraph should introduce LIGO and the science that the paper is addressing. For example, if the paper is about a highmass CBC search, the paragraph should say what a black hole is. The remainung text should state why is the work interesting, what are the main results (as you suggest below). The abstract/synopsis should be understandable by non scientists and be captivating, but should not give up rigour in favor of entertainment.
As an example, authors could look at what we prepared for the GEO squeezing
These are also few examples of the style that could be appropriate for the introductory paragraph:
http://worldsciencefestival.com/events/astronomys_new_messengers_the_exhibit (second paragraph)