So my only outstanding issue is how to get GPS hooked up and showing on screen (for surface positioning only).
You’ll need to find a compatible GPS sensor and then the serial and I2C lines go into the appropriate ports: ArduPilot: UBlox GPS + Compass Module
A suggestion, figure out a way to waterproof and mount the GPS on a mast, if that is what you want to do. GPS’ mounted internally do not work.