[Jeffr0]

This is probably conventional GM wisdom, but here's my ..02:

If you look at TV series like Serenity and Doctor Who, you'll see that they'll take an entire episode (read=> session) to explore just one aspect of a faction.

Your rough sketch of background information doesn't have to be all filled in for you to start. While you might want to have a variety of plot hooks for the players to choose from, your session only has to delve into one of them at a time. No matter how much you've planned, you'll still end up improvising. Make notes of the session... and try to think up ways to leverage the events to make new plot hooks.

When I run my games... I summarize "the story so far" so that the players can keep up. The illusion of reality comes from having logical consequences impact future sessions and plot hook options... and also in the reuse and development of previous situations and NPC's. (Think of Badger, Niska, and Yosaphbridge from Firefly.) The work is not done on the front end, however-- it is done from session to session.

And like other people have said, rationalizing mistakes can be a real source of creativity. (Give yourself a no-prize!) Players' misinterpretations can often be better than what you would have planned anyway. The reason this style of GMing works is that Players generally don't know how to articulate the nuances of their campaign preferences. If your setting adapts to their in-game choices over time, you'll invest effort where they'll appreciate it most.