IIS cannot save such settings. It will throw error.
Yes, This is perfectly acceptable and IIS will work accordingly.
No If you set the idle timeout for an application pool to a period of time that is longer than the time specified for time-based recycling, IIS will ignore the settings that you specify and instead use the default settings
YES, If you set the idle timeout for an application pool to a period of time that is longer than the time specified for time-based recycling, IIS will apply the longer time period settings.