As usual, you will identify the stages for your process, then decompose them into steps. For your scenario you can just keep it simple and have 1 stage: Intake.

Then in the stage, create 1 multi-step process to import the cases and route them to each workbasket according to your business logic.

So it can really be as simple as 1 stage and 1 step.

Please take a look at https://pdn.pega.com/integration/how-to-set-up-a-file-service-and-file-listener

• Use the case designer to define the stages and steps
• Your file listener could start this case. 
• In the "service activity" (see the pdn article mentioned above), you can conditionally assign based on the properties in the clipboard to different workbaskets. So when someone is logged in the case manager (for example), they would see the work automatically in those workbaskets