1. ALL diverter valves specify that ANY unused openings should not be capped, but are supposed to be tied into one of the active device lines.
2. Probably because of the angles required, although 45 elbows would have been better.
3. The spout is not flow restricted so it can flow as much water as the valves can produce. That is what creates the noise. The shower is restricted to about 2 1/2 gpm and cannot create the flow necessary to make the noise.