I had the same problem, but i sorted it out. I have 147 but i guess there wont be any differences. I passed the power cable through the bonnet cable hole.
Under the dashboard there is a lever you pull to open the bonnet, right? From this lever starts a bowden cable which ends to the bonnet's hook. This cable passes through a hole under the windshield area. There is a plastic/rubber housing there which holds the cable. I had widen its hole a bit with a screwdriver to make room for the power cable. It was not that easy, i had to put some lubricant there to insert the power cable from the bonnet side, to the interior. When i managed to insert it some centimeters, i grabbed it and pulled it in from the area over the clutch pedal.
About the door panel, you must unscrew all the screws and then unbutton all the clips that hold it. You have to be careful not to brake any clips (use a flat headed screwdriver while pulling out with your hand), and to find out all the screws, one or two are hidden under plastic covers.
Use much foamy tape on the door on each surface you think that the trim will touch the door when you put it in place, i did that to avoid any creaks from the doors.