I want to take a Radar Sensor with Amp instead an Infrared Transmitter.
Look at
www.conrad.de with order Code 502667 or 502370.
It gives out a voltage or frequency, when some motion is in receive Area.
I think your idea is to complicated.
I would use a FT232 Bridge ( e.g. FT232RL from FTDI ) in Bit Bang mode.
So you could control and read out some Ports that start the recording of your camera.
When frequency is present, one In- Port is high and the PC starts recording.
When frequency goes off, a short time recording goes on and then it will be switched off.
The same signal could be used for the door opener.
One little Problem is, when a person stands direct in the door without motion.
Then the Radar Sensor gives no Signal. You could solve this with a infrared distance sensor that measures the space under the door.
Additional the Power of the door mechanic should be so low that it represent no danger for a Person that stand there. Or you can use touch sensitive strings at the door's front that opens the door again when there is some touch.