With momentum building toward the development of casinos in Massachusetts, the state panel in charge of setting up the industry is looking to rapidly expand this fall with the hiring of several high-level staff members. “We’re getting to urgently need some other senior people as stuff is beginning to roll so fast,” said Stephen Crosby, chairman of the panel formally called the Massachusetts Gaming Commission. At the top of the commission’s list is an executive director, who will help shape an agency that eventually will employ as many as 175 people.