Welcome, @Sara_Y,
You’ll likely get many different answers here because none of us have enough information to know what’s right for you; that takes a long discussion in an interactive session.
If I was pressed to answer (for some reason) with only what you’ve shared, I’d say take it with a grain of salt, but consider:
Create a "[Property Name] Property” project template then 40 projects from it. Create a "[Tenant Name] Tenant” project template then a project for each tenant from it. Work to be done are tasks, perhaps with subtasks, perhaps with task templates for recurring work. Perhaps use multi-homing to handle the intersections of properties and tenants. Also create a Properties portfolio and a Tenants portfolio. Use many best practices at the task, project, and portfolio levels to achieve a smooth workflow.
Caveats: I think it’s a mistake to attempt to use Asana for a workflow of this scope without either taking a very deep dive into Asana’s features and workflow design, or hiring an Asana Partner (like me and others here). One part of that deep dive could be to watch this workshop I gave with the help of the Asana Education team:
Thanks,
Larry