Kristen Hadeed was going to surprise Josh Greenberg at a meeting Wednesday with news that their company, MaidSuite, had its first customers. Instead, the group of young entrepreneurs who have gathered every month for four years for support and ideas spoke to an empty chair, saying what they wished they had said when Greenberg was alive, his vegetarian pizza there “as if he was going to walk in and have a slice,” Hadeed told the nearly 600 people attending the Celebration of Life for Greenberg on Friday afternoon at the Phillips Center. “He inspired us to keep going,” she said.