It sounds like you have the majority of the route figured out.
And Anthony is getting you going on the AC.
You are correct about not pointing the PIR (motion detector) towards the window if direct sunlight can be reflected into the PIR. I say reflected because generally speaking the PIR will be mounted in a position that is usually high enough sunlight cannot shine directly into it, unless you have some very tall windows.
But if there is no way the light can be reflected it won't cause a problem to point a PIR at the window. The daylight alone will not interfere with the PIR. It's always best to avoid this if possible but I've done it many times over the years with no problems I can recall.
Also, PIR's do not have to be mounted in a corner. They can be mounted anywhere you wish as long as there is nothing that can cause false alarms, such as an air/heat vent.
