This probably doesn't need to be said, but Ben Robbins' marvelous West Marches series is an ever-evolving resource for players and GMs alike. Do yourself a favor and check back periodically to read the comments (and the timely responses from Ben and his players) that just keep piling onto this fantastic group of articles.
The wrap-up piece, West Marches: Running Your Own, has no fewer than 137 comments, probably more by the time you read this. They're from players and GMs wanting to know more about Ben's fantasy sandbox. He's responded to most queries, which of course prompts even more questions from his readers. You'll even find a few of my own comments mixed in among the discussion.