Bole Hotel-Transit Visa?

My wife and I (mid 60s, Chicago area) are doing a Tanzanian safari sandwiched in between some stops in Europe in February. The flight that worked the best for our itinerary is with Ethiopian Airlines traveling from Istanbul, to Addis Bole (10 hour layover), and them onto Arusha Tanzania. Even though there is a 10 hour layover in Addis, it doesn't qualify for Ethiopian Airlines complimentary layover hotel because there is another flight leaving that day with a shorter layover duration. It retrospect, I probably should have booked that flight, but to change it now is going to be prohibitively expensive. Oh well. Since it is a long flight, we would like to get some quality rest during the long layover. Is there an in terminal hotel? Would we have to get a transit visa? How big a deal is this? Any guidance would be great appreciated!