As far as my logic works, you can. The reason I am asking you to use only the auto locking pins of the ECU is that you can use your original Keyless Entry to lock/unlock the car. Yes, Civics do come with OEM central locking but you can not connect them with the security system's ECU therefore you have to put one central locking motor on the driver's side which acts as the master motor.
I am not sure, but you can pick signals from the lights that illuminate when you put your gear on "P" or "D". Basically it is carrying signal/power to turn on that light.
This information is based on my knowledge and thinking. I might be completely wrong, therefore I would suggest you to ask a professional electrician and discuss what I have mentioned.