Answer
A practical way to sequence this is to map the highest-value transactions first, the ones a customer, partner, or downstream system is already waiting on, such as order status, inventory availability, or pricing lookups, and expose those before building out a broader catalog of endpoints. Each API should be documented, typically with an OpenAPI specification, so both IBM i developers and outside integration teams can work from the same contract without needing to read RPG or COBOL source to understand what a call does.
Governance is what keeps this scalable as the number of endpoints grows. That includes a versioning policy so existing consumers do not break when an endpoint changes, a deprecation process with real notice periods, throttling to protect the underlying partition during peak load, and a defined security review before any new endpoint goes into production. Buyers should ask whether a prospective platform or partner treats API governance as a built-in discipline or as something bolted on after the first integration causes a problem, since the difference usually shows up within the first year of real usage.