Answer to: screen + digitizer differenceThere are some parts that need to be transferred from the old screen to the new screen. Here is a link to a video https://youtu.be/8PsWPNQvcTI
Answer to: Do I remove the protective cover removed?Yes, remove the protective cover on the back of the new LCD assembly. WARNING: Failure to remove the protective cover from the mirrored back of the display assembly will damage the LCD. There is a thermal pad installed on the iPhone frame that absorbs the heat from the LCD and disperses it though the frame, preventing the LCD from overheating.
Answer to: Small white square near front faceing cameraThat is the Ambient Light Sensor Filter *Black Display Only Not sure where they sell them. Maybe someone else knows.