One way to get over the challenges of biking up steep hills with a single speed is to hitch a ride from a slow (relatively) moving truck, which everybody does. Of course, going downhill is relatively easy - dangerous, but easy.
Most ex-pats are comfortable riding on the dirt roads or foot paths (some of the best single-track in the world), but riding on the paved roads is not for the feint of heart as there is very little awareness of bikers by Rwandan drivers. I've seen a number of bloody (more than one fatal) accidents. The roads are narrow and people don't give bikers (or motos for that matter) room when passing. As Kigali increases from just over a million people to 2 million (2020 projection) and eventually 4 million (2040 projection) it would be great to find ways to encourage biking and make it safer and more convenient for those that do.