Awesome -- if you want to play with the STM32F4, I recommend the STM32F411VE Discovery board[0], which seems to be in ample supply (no small feat!), works with Hubris out of the box, is pretty cheap, and has a built-in ST Link. Also, note that Humility is the debugger, but it's an entirely reasonable conflation, as much of playing with Hubris is in fact playing with Humility! We don't have too many drivers for the F4 (our SP is based on the H7), but it's a well-documented and understood part/board, so there should be plenty of fun to be had!

[0] https://www.st.com/en/evaluation-tools/32f411ediscovery.html