There is no ZMax support in the firmware for the Primo. There also isn’t a proscribed mounting solution for a ZMax limit switch. If you have figured out or can figure out a switch mounting solution, you can wire that switch in parallel with your touch plate (which uses ZMin). You then need to enable probing (G38.2) in the firmware. There are a couple of topics that explore different settings to turn this functionality on. I explore one way in this topic, but my solution uses the Z_SAFE_HOMING firmware setting, which may not be what you want.
After going to all the work of setting up the bitsetter and later Z probing up, I’ve barely used the bitsetter.
Note that limit switches are only used during homing or probing. They are not active when you are running your jobs. Ther is a potential for soft switches (to limit router movement to the working area) to be active, but the way most people set up their jobs, soft switches are disabled.
On focusing your laser: If you use black cardstock and the right laser setting, you can watch the glow of the paper starting to burn increase and decrease as you change the focus distance. I also found the spot size is the same over a larger range, though selecting the middle position of when the spot appears smallest should be very close.