just adding GPS functionality (via Bad Elf, etc.) to my measily iPad (1st gen) and then purchasing iNavx to have a fully functional chartplotter on my boat?
Yes. If your iPad 1 is a 3G model then no need to add a GPS as it already has one. No sense in buying a non 3G iPad because for a mere extra US$129 you get 3G connectivity and stand-alone GPS receiver.
In the unlikely event you find your self with a non 3G iPad then yes the Bad Elf GPS receiver is a good choice.
In this case, one can't look a gift horse in the mouth (raffle prize!). So asked differently, once GPS functionality is added to the iPad will I be able to view my vessel/travels on the NOAA charts or will I need additional hardware/software to accomplish this?
Yes once you add a BadElf to your iPad WiFi then you can turn your iPad into a full color chart plotter using the NOAA charts with iNavX.