Best practice for Contingent worker field service technician and costing billing for such resource

Summary:

Client will like to know how contingent worker fields service technician works in OOTB Oracle fusion.
How they should created? whether they should be created as contingent worker in Fusion and integrate to OFS? Or create directly on OFS?
How the costing of such resource will be done since their labor price paid to supplier will vary based on activity/tasks they are doing at any point of time.
How customer is charged on such and debrief integration works if they are not defined as Fusion worker?

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