Person manipulating the controls. Visual observer. Remote Pilot in Command (Remote PIC).

30 days. 10 days.  90 days.

Continue the mission, airplanes are not allowed to fly lower than 500 feet AGL unless around an airport. Give way and stay clear from the crop duster.   Continue the mission, ...

visual observer. remote pilot-in-command.  owner of the small UAS.

No more than three as long as the Remote PIC maintains visual line of sight. As many as he/she can handle. No more than one. 

make sure the UAS is within 400 feet of the control station. maintain line of sight throughout the entire process.   have a visual observer.

is required to receive ATC authorization.  must use a visual observer. is required to file a flight plan.