"Tenants give their address and rent amount per month in exchange for access to everyone else's data" This is a tricky game-theory scenario. It may work if all

"Tenants give their address and rent amount per month in exchange for access to everyone else's data" This is a tricky game-theory scenario. It may work if all the tenants find the value in it. It may also implode for tenants or the land-owner. "Why is there no data on what your neighbor just signed his lease for?" If the info isn't public, most people that value privacy will not want to share this. I'm not too sure about the other ideas, but maybe you need to think of something simpler, that helps address a problem that all people like you face. Maybe the best idea in this case would be the simplest.