I've been slowly making progress on design of a a hive scale. I've designed a board to fit in a small enclosure from polycase.com.
The board has an MCP3551 ADC to read the load cell, driven at 5V by a 5V regulator on the board. I could probably get slightly better resolution at 10V, but adding a second regulator isn't worth the trouble.
I did my best to isolate the load cell measurement from any digital signals, and while I'm not confident that I've followed any specific set of best practices, at least I don't have digital signals running near the important voltage measurement, and I'll also be able to ensure that there aren't any digital signals passing around on the board while the MCP3551 is taking measurements.
Even though Contextual Electronics didn't start the design course in time for this design, I didn't want to design this board using a non-commercial license from Eagle or DipTrace, so I took the plunge into KiCad. It's certainly different, but now that I have a lot more experience with amateur EDA, I've found that the KiCad isn't missing anything critical to this kind of simple design.
Here's a render of the board from OSHPark where I've annotated the different components.
As I said before, I've got the MCP3551 close to the load cell lines away from any digital signals. At the bottom right, I've also got a temperature sensor that I've thermally connected to a separate ground plane (on the back). I'm hoping I can get away with eliminating the external temperature sensor by minimizing heating of the on-board temperature sensor. I will cut power to the board by disabling the regulator when it's not being used, and I'll read the on-board temperature sensor first when the microprocessor comes on, so the sensor won't be heated by the microprocessor before taking a measurement. I still fear that the weatherproof enclosure will be insulating enough that it will retain too much generated heat from one measurement to the next, but I'll be able to determine that by comparing the on-board sensor to the external sensor.
I also purchased some 200kg load cells on Aliexpress.com. They came quickly and well-packaged, and while it'll be a few more months until I can test them for precision, they look beautiful!