It's pretty late, so this post will be short. However, I have successfully wired up and coded the limit switches into my test program! I wired and coded them as per this amazing guide. I didn't even have to use external resistors! Everything went fine and I now have code that runs parallel to the main body of code to detect button press events.
Additionally, I moved the breadboarded laser driver circuit to the 12V power supply that powers the fan and motors. Now I don't need to use my lab power supply for that job.
Next, I will play around more with code and get the real burning laser running!