On a sunny day (Fri, 27 Jul 2018 13:17:43 +0100) it happened "NY"
 wrote in :

>Are the GPIO pins hot-pluggable, or will Nasty Things (*) happen if you
>connect/disconnect anything to them while the Pi is running?
>
>(*) Either at the software or the hardware level.

No, not hot-pluggable.
Very likely you will kill the chip if you try that.
Static electricity, voltage levels above 3,3. V, wrong connection sequence,
my remark was more for when you design a board.
Also some electronics knowledge is required to interface to those pins.

There are also hats', but quite pricey:
 http://www.sailoog.com/openplotter
  https://docs.sailoog.com/openplotter-v1-x-x/tools/moitessier-hat
No connection with them, I do see they copied the idea of my little sensor
board
with compass, and accelerometer ;-)

There is a whole team working on that boat navigation stuff,
 charts are available, there is also opencpn (I have that).

Probably much more.
For me it is the fun of writing the code, understanding in depth how GPS etc
works,
and designing the hardware.
I have an electronics background, so should not make those mistakes (killed one
raspi nevertheless by shorting 5V to a 3.3V pin).

If you come more from the user perspective, then stay with the USB thing you
have, I have modified some GPS modules
by adding an ebay module for serial to USB too, works OK except for that
renumbering every now and then.

If you are into navigation, steering a boat, way points etc, look into opencpn,
and openplotter.
 https://opencpn.org/

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