I've been trying to find a way to easily duplicate projects (with the corresponding sub-projects) but can't find a way to do so. Is this possible?
Duplicating projects (include sub-projects) is not possible at the moment. You can, however, import/export tasks so you don't have to manually over re-enter your commonly used tasks/checklists.
You can refer to this link for an overview on how to use it: http://www.youtube.com/watch?v=_Rl_CLGY_3o .
If you like, you can also add this as a suggestion in our Votebox https://todoist.com/Vote/.