Tenancy is a product boundary
Multi-tenancy is not only a database decision. It defines how organisations, users, permissions, subscriptions and support operations relate to one another. Those relationships should be modelled before the interface makes assumptions that are difficult to reverse.
Make isolation testable
Every request, background job and integration needs an explicit organisation context. Isolation rules belong in shared server-side boundaries and automated tests—not in conventions developers are expected to remember.
Design for operations
A SaaS product also needs tools for support, auditing, plan changes and incident response. Building these operational paths early reduces risky direct database work after customers arrive.