One of the most difficult things in constructing a Hard Science Fiction campaign is dealing with the implications of scientific developments. This is why I tend to defer to novels and to established SciFi settings when running games.
In the RPG Traveller, communciation could only travel as fast as the fastest mail ship. Message transmission goes only as fast as the speed of light, while ships can travel at FTL speeds. This lack of "faster than travel" communication resulted in a semi-feudalistic structure of the Empire. Local Governors / Warlords are responsible for the sections of space that they can control, and are allied to the Emperor. This results in an even greater variance in the laws and trade agreements than would be present in an already homogeneous, monolithic empire and makes it difficult to figure out how to navigate the web of trade.
How does the galaxy keep from falling into chaos? Trust, politics, detente and diplomacy, plus the occasional "police action" or "black op".