Jonathan Gray of Blackstone Group LP went on the biggest homebuying spree in history after the U.S. foreclosure crisis, purchasing repossessed properties from the courthouse steps and through online auctions. Four years, $10 billion and roughly 50,000 homes later, he will find out if his gambit will pay off. Invitation Homes LP, the Dallas-based company Blackstone formed to maintain and rent those homes, has filed confidentially for an initial public offering that could come as soon as January.