Permissions and structural concerns aside, you only need one 65mm/2.5" hole in the wall to run the high/low pressure gas lines, a drain hose, and a power cable, plus couple more non-penetrating drill holes on the wall to mount the inside and outside units. You'll need a hole saw attachment on a drill, a vacuum pump to thoroughly dry out the system, and bits of plastic putty to fill the hole against intrusion. It's a less than 5 man-hour job.