laser inside wont mess it up.
it is actaully a good idea as the GPS will sit on the metal chassis of the HU which will act as a grounding plane and improve reception.
but check you get signal on your dash 1st as you may have a metal tinted windscreen.
I would try taking the top cover off your GPS and seeing if it will fit.
as for NMEA - that is the data stream most GPs use to communicate - dont worry about it
and as for the virtual com port - dont worry about that either. It just turns the USB you are suing into a virtual com port so the software looks at it for the nmea stream - makes life easier. If you move usb ports you may have to change the com port setting in the software though as it may assign a new virtual com port number to the different port.