I have been plugging away at trying to match enough hardware to this MCU to achieve the functionality I want.
Some would say resistance is futile,
some would say persistence is fertile,
I would just say persistence takes a while.
Currently I found a card that has a LoRa radio and a GPS, from Dragino, that should fit with both the Nucleo MCU and my custom card.
The Dragino card is an arduino compatible card and there is some arduino software that runs it - if I can port it to the Nucleo.
Fortunately ST Micro has been working to get their STM32 cores into the arduino board manager. The instructions on how to install STM cards in the arduino IDE are located here. If you are familiar with arduino programming you can dramatically step up performance with this 80MHz 32bit Cortex M4 platform (1 Mb FLASH, 128Kb SRAM, 12bit ADC)
Here is a short video demonstrating that the arduino IDE works fine with the Nucleo L476RG - one big hurdle cleared:
Blinking LEDs is not usually a big deal, but it represents getting the software development system working properly with the target platform and I am extremely happy to reach this milestone.
My custom expansion card with LCDs and sensors was designed before I settled on this solution, but luckily the pinouts are quite compatible. The main problem might be that the LCDs cover the GPS antenna, so I may need to mount an external antenna. (there is already a convenient connector for this scenario)
Now I can start diving into software development. There are still significant risks and uncertainties remaining, not to mention lots of work, but I am light years ahead of where I was when I had no fully functional design.
This has been a short update but lots of work went into clearing a major pin conflict roadblock and an important development system milestone has been achieved.