Philadelphia is home to nearly 2,000 professional dancers who use about 20 rehearsal spaces and 45 different performing venues. Those dancers and the small companies they work with want to build a home where they can work. Wait for it, warns a new study. “The primary issue, the study said, is that most of the city’s dance groups are tiny and do not have the business side of their operations in order.” It advises waiting three to five years to get better established.