Excellent, I'll stick with my lofty smart watch goal then. I do have some intermediate steps like running some sensor fusion from an IMU in real time. So hoping I can build up a system, add peripherals, then transfer off a dev board, then keep iterating and adding complexity over time.
Rust looks very cool and is probably the future. To lower complexity it seems to make sense for me to stick with the familiarity of C from a bunch of Arduino projects (Although mostly Arduino IDE and Libraries) and some C++ projects (not embedded), but maybe I don't know what's good for me there, is there an equivalent to shooting yourself in the foot or blowing your whole leg off in Rust?
It seems to make sense to dabble with registers enough to be confident in understanding what the HAL is doing whilst learning, I find taking a peek at the lower levels of abstraction can really impact how to use libraries best?
"Reference Manual" - Brilliant! Just took a look and this is going to help me get my bearings so much, thank you!
STM32 family is definitely overwhelming - I was tempted to pickup a F0 Nucleo to match the tutorials but I'll take that advice and stick with the F1 Nucleo that was given to me.