From what I know now I would have made several different hardware choices. For instance:
1. I initially blew off the Adafruit ribbon connector from the Pi's 26 pins to the breadboard. It didn't take long for things to get really messy (and it led to wiring mistakes).
3. Here's a device that has caused me grief -- it won't stay connected:
4. I certainly learned something, but controlling a solenoid with a transistor was a lot more trouble than using a Darlington array -- and the array will do 8 devices:
5., 6. I suppose every Pi beginner starts with buttons and LEDs. I mentioned (back many episodes) that I didn't know that polarity mattered with LEDs, but I got over that. However, the buttons I bought don't stay put on the breadboard. Half the time when I release the button it jumps out of its socket. Luckily, I've learned to control the Pi -- first from SSH and now from a Web page.
I also got some 3-wire spring connectors (hopefully to make reliable connection to stripped wires). That probably works but do they ever waste breadboard real estate.