Addis 3 day visit

I am spending 3 days in Addis Ababa in February on my own. I have never been to Ethiopia and have some pretty basic questions. I do have a reservation at a guest house and will be picked up at the airport. I have to pay for the guest house in cash (no credit cards accepted.) I have an ATM card with no ATM fees and no foreign transaction fees. Will it be easy for me to get the cash I need to pay my bill at the guest house via ATMs and for other expenses in Addis? Should I instead have enough cash to change into birr at the airport or at a bank in Addis? Which is the best place for exchanging money -- bank or airport? I have heard that the Hilton is a good place to exchange money, but I do not know how convenient that will be to where I am staying. I would also appreciate any suggestions for the best use of my time. I have asked the guest house to arrange a 1/2 day tour the day I arrive. I also hope to book a full day tour to Debre Libanos monastery. I would appreciate knowing which tour operators folks you have used and how much the tours cost. Would you recommend the same tours and operators to others? Thank you. Moderator's note: This is actually a posting by "travelgeek" (not Marian) which was inaccurately posted as a reply in someone else's post.