You could copy the low voltage buck from my Gooser4. It only uses two extended parts (the nearby TVS diode SMM4F26A is not part of the buck converter). It was designed by @Valentine on his Mosquito, and I’ve rearranged it a bit and reconfigured to output 4.3V which I then regulate down to 3.3V for maximum stability. Mosquito has it output 3.3V and uses that directly, which would probably be fine for you as well since you’re not using 3.3V analog sensors. Replace R1 with 33k to output 3.3V. EDIT: On second thought, the bluepill has a regulator onboard, so stick with the 4.3V.
Unfortunately Valentine has taken his designs offline for the time being, but hopefully he doesn’t mind me sharing fragments of them I copied in the past.
Regulating 24V to 3.3V would be wasteful, but I think it would work. I’m not sure about F103, but STM32G431 uses around 35mA, which is 21.7V*35mA=76mW of heat. The bluepill board has some LEDs that will use more, but the datasheet says that regulator can survive 500mW so you should be ok, especially with a fan blowing on it. EDIT: Calculation error. It’s 760mW, not 76. The regulator will burn up.
P.S. I’d stick with JLC basic parts for the capacitors rather than trying to ensure that they all use the same package size. Larger packages are easier to handle for manual assembly, but irrelevant if JLC is doing it, and extended parts fees add up fast.