Arduino uno and mega

A project to control multiple doors. The number of door varies from 3-30. I intent to use one UNO for each door in a One master and Multiple slaves arrangement, signal is loop via one wire. On each door, there are: 1) Three LED light. to indicate "RED" for not allow to open", "Green" for allow to open" and "Yellow" for fault' 2) Logic for the light is: when all the doors are close, the green light on, when one of the door is open, the red light on, and if the door is open for longer than a preset time (say 10 sec), the yellow light on. 3) each door will have one Limit switch to detect the door status (close or open)."ON" means close and "OFF" means open. 4) each door will have one push button. push button when activated, will de-energized a relay for a preset time (say 6 sec) to open the door. and relay will re-energized automatically after a preset time (say 6 sec). 4a) In an initial stage, all doors are closed, and relay energized, all lights Green. 5) each door will have one buzzer, buzzer will energized when the door is open for more then 10 sec , the buzzer sound will cut off when the door is close. 5a) buzzer will sound only at that particular door that is open, all other doors will show yellow light. 6) At any one time, only one door is allow to open, first come,first served basis. On master control. 1) Three LED light. to indicate "RED for not allow to open", "Green for allow to open" and "Yellow for fault' 2) Logic for the light is: when all the doors are close, the green light on, when one of the door is open, the red light on, and when one of the door is open for more than 10 sec, the yellow light on and a buzzer sound. 3) a toggle switch to select between "normal" and "all closed". when "all closed" is selected, all the doors cannot be open. i.e. the button on all the doors are disable. Additional Wish list : 1) a seven segment at the master controller to indicate which door is open. 2) the slave at each and every door are self-registered with the master. i.e. replacement of the slave controller is plug and play. 3) expansion of the slave controller is plug and play when new door are added.