I would be also interested in your itinerary. If you don't mind sharing, maybe this can be public information?
I did the Northern Ethiopian trip in 10 days. The main places I visited included Hafar, a walled city that is a UNESCO World Heritage Site. From here we travelled into the Afar region and visited the Danakil Depression, Erta Ale and Dallol. Then we head towards Lalibela, a small town famous for its rock cut churches and finally back to Addis Ababa. If you are interested in tribal cultures, then go to the south. But that trip is another 10 days and most likely involved camping in the bush. I have pm'ed you contact details in Addis Ababa.