After some soul-searching, I decided to upgrade the project to the Arduino Mega, shown here. It just arrived today. Surprisingly, it’s still very small (4″ x 2.1″), but has eight times more program memory, and eight times more RAM, which I think I’m going to need. It runs at the same clock frequency, 16 MHz. It’s got more I/O than I can ever use. But I’m tempted to try!