A3 8P optical parking kit

Keep my eye on this thread.

You would want to get yourself the OEM sensors and a bumper that already has the holes for it as those bumpers also have the brackets that are used to clip the sensors into place. Also remember that the front sensors also require a new grill with the sensors built in. You need the OEM sensors so that the car can communicate with it to get the actual visual distance on the rnse. The first link you have there looks like it has the right bits but if you already have the rear sensors then you already have half the install in the car and just need to add the front sensors.
The parking module sits on the right hand side of the boot behind the carpet.
to pass the wires past the firewall you can either follow the bonnet release cable and pass the wires where that goes or pass it through under the scuttle panel and under front wiper motor so it goes directly into the central electrics module area.
you will then only need to lift up the sill trims ao that you can pass the wires under the foam to the back of the car to the parking module