It didn’t take long for Hollywood’s newest movie studio, Summit Entertainment, to reach a crossroads. The 2 1/2 -year-old company, riding high on the teen vampire phenomenon “Twilight,” is hoping to leverage that success and avoid a premature demise that has befallen many mini-studios. While market pressures are forcing rivals to retrench by slashing overhead and reducing the number of films they make, Summit wants to go the other way: expand and increase its output of content. Start-ups are difficult even in flush times. But Summit’s planscome at a perilous juncture for Hollywood’s majors, roiled by declining DVD sales that have undercut movie profits and monumental changes in technology that are reshaping how people watch entertainment. Other independents, such as MGM and Weinstein Co., are scrambling to stay in business, while several studio-owned specialty film labels have ceased operating.