Don't you just love breakthroughs? I was looking at the Network mapping data I had and swapped some columns and realized that it is in fact a grid of 7x8 (at least electrically) plus the on button. It's just not arranged physically in the same grid that it is electrically, but it still the same. That means I have the option of using the GPIO-Matrix Device Tree Overlay like I originally wanted.

I received the second USB port and have decided to go with the Adafruit one. The contacts are better and I think the shape works better, but in all honesty, I think either would have worked out just fine.

One of the things I realized is there isn't a good way to check the battery level with my current design. I found a project that allows you to check this, so I ordered an MCP3008 A/D converter that I'll see if I can connect into my project. It really depends on whether I will have room in the calculator case.

I looked at the spreadsheet once again and with removing the audio board, it looks like I'll now have just enough pins because I was planning on using one for either the low battery output from the PowerBoost or the MCP3008 chip. In the event I don't have enough pins for my needs, I happen to have a 74HV595 shift register that I could hook up for checking the keypad that would free up 4 or 5 pins depending on how I decide to connect it. Space is the main issue and I don't believe I'll need to use it since the MCP3008 communicates via SPI and I only need 1 extra pin for the Chip Select. My main concern on that is the Display uses SPI and I don't want there to be any conflict and that will require further investigation.