remote start system suggestions

Maybe you could use this diagram to add on some extra channels to the usual single or double channel remote starters.  You can find this on this website's Relays, Special Apps page.

One Channel to Multiple Outputs

It uses a little bit of ladder logic.  You can set it up to trigger a different output when the car is running than when it is not and things like that.  Not all would happen at the same time. 

I don't know if that will help because I think with most of the things this customer wants the car has to be turned on for all of them, right?  Unless you were to power the windows and sunroof through a relay connected to the remote start system.  You could maybe get away with hooking things up to control the defroster when the car is running and control the windows and sunroof on the same trigger when the car is shut off.  This way both the windows and sunroof would open at the same time.  I don't see a reason you wouldn't want your sunroof open and not your windows.

Otherwise, like Teken said, you can set it up to work for different outputs by physically switching toggle switches in the car.  That way you wouldn't be able to use the remote to control all of the features at the same time.  This would work too because I don't think you want to use your defroster in summer or your windows and sunroof in winter.

Both ways would seem to work for me.

Yeah, you don't want to use the factory remote.  I don't see why someone wants to stand on top of their hood to start or unlock their car with a remote.  It looks like things should work out.