I just added a link to the new project on GitLab! Now everyone else can actually access the code and the Fritzing sketch for this project.
In other news, I'm still trying to figure out if one of the OPA4228PA I have on hand will suffice for reading the temperature sensor in the RT tip, or if I need to wait for the OPA344 that was used in @banjohat's project... The OPA4228PA isn't rail-to-rail, but it is "high precision, low noise". I'm going to try breadboarding it and see if I can get it to give me useful results.
Also, I realized that the common anodes on the LED display will actually each need a transistor to drive them, possibly paired with a resistor to limit the current. That makes things significantly more complicated, since it only seems to work if I use PNP transistors, and I only have 2 of them that actually do anything in the circuit right now. Looking at the possibility of a Darlington array chip (and maybe also a resistor array) to keep component count down.