Recurring tasks that have subtasks associetaded
How to manage a task that need´s to repeat, and as subtasks associated to it?
Should the subtasks have a due date (can it be a different due date)?
When completing the parent task and/or all subtasks, what is the result to expect?
it depends on whether you want a complete set of tasks to recur or just the main task or just one or more sub-tasks.
Basically, if a main task is non-recurring (with a fixed date or no date at all), then even if its sub-tasks are recurring, the whole structure will be moved to history (to the "Show completed tasks" list at the bottom) and removed from your project, at the time when you complete the (non-recurring) main task.
On the other hand, if the main task is recurring and the sub-tasks have fixed dates (or no dates at all), it will never be removed upon completion and neither will the sub-tasks. They will get a check mark, though, once you complete each of them.
That said, it depends on how you'd like to plan your work and which parts of it will be repeated. If the complete set of tasks is recurring, you can set the whole structure with the same formula (even at once, by pressing the Ctrl button and while holding it, selecting multiple tasks by clicking on them and then choosing "Change date" from the blue menu bar at the top) and although recurring tasks won't be removed, each completion will be shown in the "completed tasks" history (available only for Premium members).
Please refer to this page:
to see which date formats are supported by Todoist.