Advertising giant WPP Group has hired the first CEO for its Dell-only agency, which is taking over the work of about 800 firms that have been coordinating ads and marketing for the PC maker. Torrence Boone, who is leaving his job as president of the Boston office for digital marketer Digitas, will eventually oversee about 1,000 employees at Project Da Vinci, the temporary name for the ad agency that’s been created to serve Dell. So far, the agency has hired about 500 employees. Boone, who is 38, is set to start work in June out of the New York headquarters of Project Da Vinci. Before working for Digitas, Boone was vice president and general manager at interactive marketer Avenue A. Last year, Dell signed a three-year, $4.5 billion contract with WPP to consolidate its ad and marketing efforts within one central agency. In addition to the New York headquarters, Project Da Vinci will have offices in Austin, Miami, and San Francisco, and will also work out of London, Sao Paulo, Singapore, and Beijing.