Re: Step 1 done
"But...no one has yet established they travel at the speed of light"
Yes, as far as I'm aware this was a pretty contentious argument throughout the 20th century, with no-one finding any concrete evidence either for or against the idea. However IIRC an experiment in the early noughties involving the observations of a quasar as it passed behind Jupiter found strong supporting evidence that gravitational effects propagate at approximately the speed of light, though I think it was also argued that what was being measured was actually the speed of light, and not gravitational waves. Hopefully these latest experiments will help clarify exactly what the hell gravity is and how it works.
On a less serious note, I wonder if the boffins involved have been the very first people in history to hear the whalesong of the universe, and if so, should I start investing heavily in really, really big joss sticks...