Use one specialist when the team can absorb the role.
Staff augmentation works well when the client already has product direction, technical leadership, delivery routines and enough adjacent capability to support the new person.
Use a dedicated team when the work needs its own shape.
A dedicated team becomes useful when several roles must coordinate closely around a product area, platform or defined workstream—and when adding them separately would create management overhead.
Look at dependencies.
If the work depends on multiple client teams, systems or approval paths, a dedicated external group still needs strong interfaces. A team is not automatically autonomous because it has more people.
Sequence capacity instead of filling an org chart.
Discovery may need a senior engineer and product counterpart first. QA, DevOps or additional development capacity can follow when the architecture and delivery path are clearer.
Review the model as the roadmap changes.
Start with the smallest useful structure, measure whether ownership and flow are improving, then add or reduce capacity deliberately.