> Also, Arduino is not the only game in town. I recently bought two Nucleo G431KBs...
ST's development boards are great. They're fairly inexpensive, especially in the Nucleo line; they cover an extremely wide range of microcontrollers; they come with real debug probes, not just serial ports; and many of them have Arduino-compatible pinouts and/or are supported by the Arduino IDE. Plus, they've got their own Eclipse-based IDE which you can graduate to once you've outgrown the Arduino framework.