I'm looking for a good resource for learning to use the STM32F0x series.
There is the datasheet, programming manual and reference manual, (..)
Are there any good books, comprehensive tutorials, online courses etc.?
I'd start from listing of thorough understanding of ANSI C (and friends), then comes tweaking of the toolchain (that is: compiler, linker, librarian, simulator, debugger) and accompanying environment (at least: make, version control and unit testing suite). After that there is the underlying Cortex M core (M0 in your case) and finally the peripherals on top.
If your question is about the peripherals then bare metal Standard Peripheral Libraries (SPL) from STM are quite easy to understand and well documented, each peripheral comes with number of dumb 101 examples.
However, Cortex-M are designed to operate with OS (to reduce development cost) so bare metal SPL clearly stands in contradiction with that. You can Hello World or blink a LED with SPL but forget about running multiple threads on one uC with SPL - no concurrency, no reentrancy, no resource protection.
So STM released the Cube version of peripheral libraries that do support OS environment (with protection) and although you can theoretically use Cube for bare metal and ignore the OS mechanisms involved, that is not what it was designed for. Using Cube requires deeper understanding of what is going on than dumb SPL because it involves a lot of OS-necessary code (that can be ignored or even commented-out for bare metal stuff).
If you are already proficient in underlying vendor-independent stuff then I'd suggest the SPL and examples there as next.
EDIT: The new OS-aware peripheral library from STM Cube is called "HAL Library", which stands for: Hardware Abstraction Layer.
Whatever.