Teams often build a single-client application and plan to make it multi-tenant later. That rewrite is almost always bigger than building it right the first time.
Isolate at the query layer
Every query carries a tenant id, enforced centrally, not remembered by each developer.
Plans and quotas belong in the schema
Message limits, user counts and storage caps should be data, not code.
Build the control room early
Creating a tenant, suspending a defaulter and reading usage should never require a database client.
Building something similar?
We will tell you honestly whether a ready product fits or you need a custom build.