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. 

Equip the aircraft with a remote ID broadcast module. You must purchase a new drone to comply with Part 89.  Older drones are grandfathered in and don’t need to comply with Part 89.

Yes, as long as the aircraft is equipped with an anti-collision light visible from 3SM. Yes, as long as the sUAS is equipped with Remote ID.  No, only transiting flights are ...

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

filed a IFR flight plan. received prior authorization from the controlling agency.  received prior permission from the commanding officer of the nearest military base.

Fly as a recreational flyer until you pass the recurrent training online with the FAA.  Continue flying as a Remote Pilot, there is a 30-day window to take the recurrent. Fly ...

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