first, welcome to the community
I don’t know Apache Nifi. But there are two ways of interacting with Zeebe:
job workers - get polled by the workflow instance (i.e. to do something)
messages - publish a message/event to trigger the workflow instance (i.e. something happened)
It depends on the workflow that you want to model.
Please keep in mind that Zeebe should be used for orchestrating your workflow but not for storing your data. If you have bigger data then the data should be stored externally and only be referenced in the workflow.
Does this help you?