A SaaS product needs a stable foundation, but that does not mean building every possible platform feature before users can solve their first problem.
Define the tenant boundary
Decide what belongs to an organization, which records can be shared, and how every query enforces that boundary. This is a product decision and a security decision.
Make authorization explicit
Roles should map to real responsibilities. Permission checks belong close to the protected action and should be testable without depending on interface visibility alone.
Build the smallest complete workflow
Finish one useful path from entry to outcome. A coherent vertical slice reveals architecture and usability issues earlier than a wide collection of partial modules.