checkboxes - Multiple or Single Checkbox for ToDo List?

Would you suggest for a To-Do List section of a project management app I am working on have multiple checkboxes?

Or keep things simple and "common" using single checkbox?

I think that multiple checkboxes will show milestones/stages in a task clearly. But if I were to want to assign due dates to them it becomes a lot more complicated both from a UI and development stand point.