Regarding domestic flights in Ethiopia, it is important to get a print out of your actual ticket (not your itinerary) to show at the check-in desk, as the Ethiopian airlines computer system at Bole airport is poor and glitches may mean they cannot find your booking (as happened to me and they wanted to make me buy a new ticket) and several provincial airports (Gonder, lalibela, Axum) dont have the computers working so if you only have an e ticket they may not be able to confirm you acutally have a ticket. This is mostly an issue if the tickets were bought out of Ethiopia since in Ethiopia they will always give a print out.
There is free wifi available at Bole airport in the transit lounge ( a very pleasant surprise) but once you go through security you will lose the signal.
It is reasonable to get to bole airport from down town in a blue cab for around 100bir but coming into the town from the airport you will be pushing to get that price and the yelllow cabs will rarely go under 150b. Even the blue cabs will try and quote you prices in the stratosphere but you should be able to get them down if you have walked to bole road.