Re: Arduino + MCP9600 + thermocouple help needed

To Richard:  The IDE is the computer host program that communicates with the Arduino. Input pullups are generally harmless except on analog inputs making measurements.
I haven't seen a floating input cause an overheating problem on a device released for production but I have in R&D where I found the resulting hot spot on the chip with a microscope and infrared camera.
https://www.waferworld.com/post/what-is-a-wafer-prober
Inputs and outputs have normally reverse-biased clamp diodes to (+) and Gnd, either inherently or for static protection. An external High signal on a pin when the device isn't powered up will pass through them to the device power supply and try to power the board and charge its bypass capacitors, which may damage the pin or the signal source. This means one switch should control the power for every board in the circuit.
Some power supplies don't take well to externally applied voltage on their output when they are turned off, or higher than their set point. This is mainly a concern when using them to charge batteries, also some consideration in bench test setups.
Hot-pluggables like USB have (or should) built-in surge current limiters to prevent damage or voltage dips in the source. They may be a series "thermistor" whose resistance increases sharply when they warm up. Otherwise plugging in a USB device could crash the computer. For USB2 the current limit is 0.5A, with some brief overload capacity to charge capacitors. If a USB-powered board and whatever you add to it draws more current the USB 5V output may drop and the board not work right.