Patrick - You can help in wherever you see needed improvement to D.C. United articles, and help one of the primary goals, which is to make the main Wikipedia entry on United an FA. From what JonBroxton has said, he's dead on. We should emulated the style of writing and content used in the Sounders FC entry. It's written in American English, and has numerous sub-pages that are also featured articles and or lists. 
 JonBroxton - I completely agree. The Sounders FC entry is easily one of the strongest MLS-related entries on Wikipedia. The American English style of writing and the specific angle focused on the American version of the game. And by "league-specific", I'm presuming you mean the MLS Cup Playoffs, the "regular season", and how the playoffs are not a cup tourney but rather a culmination of the regular season? 

And re: stadiums, that's probably a great way to start. Also, with the format of MLS articles, perhaps we can work with the Sounders FC task force to create an article format that's idea for MLS clubs and within the guidelines of the WikiProject Football.