Not quoting from any texts but from experience.
The first one,
No, flown a 2 bladed C207, noisy as, flown a 3 bladed C207, quieter.
Second one, it's the size that can absorb the power.
Higher tip speed, no, more blades = slower = less noise.
Too many blades interfere with the airflow for the next blade.
2nd question. Someone else can answer it using far more technical language than me.
Prop blades have pitch too, not just the aircraft.
If you coarsen (or feather for twins) you certainly improve the L/D ratio because you are reducing the drag. This will also reduce the RoD.
I am sure your lecturer should be able to explain this better or someone else who's more technical than me.