No the bumper didn't have to come off. I literally did it within 90 minutes of collecting the car from the dealer. If you look behind the bumper there are some supports, but where you fit the sensors there is no backing. You literally cut the holes, push the sensors into place and feed the cables through the grommet in the spare wheel well in the boot. Plug the four sensors into the control box (they are labelled to say which is which), connect the power and your done. To keep it neat use cables ties and where the 4 sensor cables some into the boot wind insulation tape around it to form a loom upto the control unit.
There is no template, but I took the measurements off the showroom car with factory one's. I can easily sketch the key measurement to you on a drawing.
I have the expensive factory one's on my Land Rover and these are just as accurate at picking up obstructions.