Yes engine and gears are more precious, but you will not harm them as along as you are keeping below the red line and you are doing it smoothly, not jerking the system too hard. In local cars i'd suggest at least 1,500 RPm below the redline would be ok.
Completely wrong assumption. The revving of engine without pressing the accelerator pedal does not equal more fuel consumption.
Actually, it might be even less than idling.
You see, when you are accelerating at a high RPM, the power of the engine is being delivered to the wheels through the clutch and transmission, the power of the engine comes when you burn fuel, hence more fuel consumption.
On the contrary, when you are going down hill, while the clutch is engaged (pedal not pressed, car in gear, not neutral), it is not the burning of fuel that is revving the engine, it is the force of gravity and your forward momentum that is moving your wheels which are connected to your crank shaft through the clutch and transmission. So here the gravity and forward momentum is causing high RPM, not fuel.
This is why we have better fuel consumption while going downhill and on the highways, even with high RPMs.
Correct me if I am wrong.