"But maybe there is a module out there which does exactly that or at least link the tasks with each other."

==> do you have an idea where I can have a look??

Thanks

Well, at the moment you can set a hierarchy (delegation) of tasks but there is no mechanism like linking, blocking, etc. (known from JIRA and other project management tools) for now. But maybe there is a module out there which does exactly that or at least link the tasks with each other.