PF,
If you are preparing for your JAR POF exams these are the answers you need to know.
Rear mounted engines reduce the ptitching and yawing moments caused by power changes and the handling problems following engine failure. The down side is that they also require stronger wings, because wing mounted engines provide bending relief and flutter damping. Rear mounted engines are also more likely to surge when the aircraft goes into deep stall.
Winglets react with the wing tip vortices to produce a total reaction that is angled inwards and forwards. The inward component is unimportant, but the forward component adds a little thrust to reduce the effects of induced drag. Because the winglets extract energy from the tip vortices they also reduce the vortex intensity. But (existing ones) cannot be moved in flight, so they are most efficient at only one speed. They are therefore tuned to provided greatest effect in the cruise, where the aircraft spends most of its time.