As a general rule of thumb, always use the biggest engine the kit recommends. Wing loading, not power determines the plane's stall speed, (the slowest it can fly). The lighter the plane is, the slower it can land. Usually when you use the smallest engine recommended, you end up adding lead to the nose to get the plane to balance anyway so you really don't save much weight by going to a smaller engine.
I have found that the large engine flying mostly at half throttle or so will usually burn less fuel than a small underpowered engine that must constantly scream at full throttle just to keep the plane in the air.
Underpowered airplanes are harder to fly than overpowered airplanes.

There's nothing wrong with bushing engines. Your car has a bushing engine and modern cars are going up to 300,000 miles before needing a rebuild and it's usually not because the bearings are worn out.