Find a mentor, someone who has hosted charity golf tournaments before, and ask for as much guidance as possible. Likewise, let the golf course pros do some of the "heavy lifting" since helping organize these events is part of their job.
Don't get too ambitious the first year. Better to start small and build in succeeding years than to take on more than you or your group can handle. A badly run event can turn off sponsors and golfers who want to be involved in a well-run tournament.