How to process array(list) of strings?

Hi all!
I’m new in Camunda. I have a project on .NET. I’ve figgured out with external tasks and interract with Camunda through the REST API. I can’t understand how can I process an array or list of strings. I need to give to instance a list of strings. It can be json array or delimited items in string. Then in Cammunda instance parse it and give each item to service task. If in service task appearing error - put this item to the end of list. If no error - delete from list. When list is empty instance terminates. Can someone give me some advices:

  1. What forat of list will be better: json or something else?
  2. How to create a part of BP where task will give each item to service task? Something like loop for-each.
  3. Can service task be a multi instance? For example 5 items processing in parallel.

This is a schema of my thinking.

See the example here: Pattern Review: DMN Looping for Array Input

The use of a DMN is the same usage with a Service Task.

You can create a Collection and/or a Json Array