I've been working on the code last few days, mostly to get NuttX to reduce power to a minimum for the STM32L476. I'm playing with various settings such as core clock speed and different sleep strategies. On preliminary tests, it would seem more efficient to not lower the clock too much so that when the MCU wakes up it does it's work really fast and goes back to sleep. I realized that updating the screen will be what mostly determines the time I stay awake, since this would be the slower operation, so I'm also optimizing that.
So far it would seem that I can get to around 2mAh while running, which would only but for less than 100ms for every second and then sleep while consuming just 7uAh. This is just the MCU though, but the rest of the devices do not use much current either and can sleep a lot.
Anyways, here's a pic of my (messy) test rig showing the screen displaying some fake data. I must say it is really readable, even from an arm distance.
Next goal is to program the low power timer in counter mode to read the wheel sensor even during sleep. I could then test it with the sensor on my bicycle and get some real data.