GTD can be implemented in Asana in many ways. How you could best implement it in your case might depend on factors such as how deeply you use Asana in your organization, how well versed in Asana your users are, how rigidly you want to implement GTD, and many other factors.
One good approach is found in this video. You’ll have to recognize that the Asana UI has changed in appearance, but not drastically in functionality:
Some alternate ideas are presented here and give you an idea how different implementations are possible:
For private tasks, you may consider using My Tasks Sections instead of separate projects, depending. For more on My Tasks, see my article:
Finally, as a nonprofit you may be interested in joining us here sometime: