Is it normal when landed and idling for one of the props to be visibly slower in comparison to the other three?
What is the cause of the aircraft to slowly migrate forward/backward or up/down while hovering in the air trying to take a still shot?

I'll let someone else tackle the drift, but you should NEVER land and not shut down immediately.  It has been reported that when landing without shutting down, many have had the bird take off again, resulting in a minor crash.  When you land, use the left stick to let it down to the landing spot, and as soon as the gear touches down, pull all the way down further on the stick to shut it off.  If you want to idle on the ground for some reason, it is generally safe to do so right after startup.  So, say you land and shut the motors off, but you want to check the battery numbers or something else while running.  Just land, shutdown, restart, and let it idle.

Hi ,roofman
Please comfirm your aircraft is working normally in the air . When your aircraft hovering , the GPS and the IMU data are calculated by the main controller in your drone . After the main controller collected these data , it will controll the ESC thus adjust the angular velocity of the motor . The angular velocity of the motor decides the forces on your aircraft . And with the GPS help , it finally makes the aircraft hover .Please search relative tutorial on youtube .