The short answer
What should a property management website show?
Property managers answer the same questions all day. Tenants want to know how to report a leak, where to send a form, what the parking rules are. Owners want to know what you'll do for their building and what it costs. Prospective renters want to see what's available. Your page answers all three groups, so your phone rings less.
For renters, that means available units with real photos, rent, move-in date and a way to book a viewing. For tenants, a maintenance request form that takes a photo of the problem, plus the building rules and documents they keep asking for. For owners, a clear page about your services and how to get a management proposal.
In the buildings themselves, a screen in the lobby can do the noticeboard's job: water shut-offs, elevator maintenance, move-in days. Changed from your desk, not taped to the wall.