This may seem like a silly question but I'm still learning.
Can you use a single mech coin door for a multi player control panel?
Encryptor
Yes and No.   Over the past weekend, I have notice a few games that had problems with 1 coin door/button.  Luckily for me at least, my 4 player cp each had 4 button and none of those games ever used the 4th button.  Pretty sure you know where I am going.  
For those games, I just assign the 4th button to the coin for the 2nd, 3rd and 4th player.  So far I have had only needed to do that to about 2 or 3 games.