FAA Regulation

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. 

The FAA does not allow the use of ADSB-out for sUAS. Anytime you are flying in controlled airspace. Only when flying in a Temporary Flight Restriction.

The applicant must have logged 20 hours of flight time. The applicant must be a US Citizen. The applicant must be at least 16 years old.

Land the aircraft as soon as practicable.  Activate the aircraft’s navigation lights. Notify the nearest FAA Air Traffic facility.

Only when visual observers participate in the operation. Alone, if operating during daylight hours. Under the direct supervision of a Remote PIC.  

It must not contain exposed rotating parts that can lacerate.  It must not contain exposed rotating parts that can lacerate and must not cause injury equivalent to 11 ft-lb of kinetic energy.

Finish the mission by paying extra attention to the surrounding. Land as soon as practical and determine if the mission can be restarted without a Visual Observer.  Continue the mission without ...

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