You will probably need to ensure the nRF24 and the ESP8266 use different frequencies (channels in nRF24-speak). I have no idea what frequencies within the 2.4GHz band the ESP8266 uses.
All of the drones I have with WiFi video allow the phone to connect directly to the drone.
You could do all of the flight control work you desire, with zero interaction with the video streaming system.
Just a note, using WiFi streamed video to fly FPV sucks. There is enough lag that it is almost unworkable. Great way to sell toy-level drones to the masses. But if you are looking to fly by watching video rather than directly watching the drone in flight, then you need a better video feed. Look at the current Fat Shark 5.8ghz equipment to see what is used by people who want to fly by seeing what the drone sees.
Good point. I am in the USA. Admittedly, I have little actual knowledge of the law.
I am a member of the AMA and do my best to follow their guidelines.
All of the FPV flying I have done with my toy quads is indoor or in my back yard.
I have several friends that fly sport and professional level quads.
Most fly at FPV racing events with no visual observation.
The guy who do professional photography took tests to get some certification. He maintains line of sight and uses the ground displays to help frame the scene.
Edit: To stay on topic, trigopatata, the Arduino is poorly suited to handle video data streams.