As already mentioned most folks will use LightBurn to drive the machine for laser jobs, because that’s just more convenient.
However LightBurn is 2D (which admittedly covers 99% of laser jobs), but I found at least one case where I had to use a regular G-code sender (CM or other) to move the laser around, and that’s when lasering a curved surface. Example in this thread.
If you have a BitRunner, yes, deactivate it (or with the new BitRunner v2, just don’t activate the enable button), since both the BitRunner and the laser rely on the same PWM signal and the router would otherwise start
Yup, if you now the offset of the laser point from the router axis center, it’s a simple matter of a G-code oneliner. Or, use this method. There are a few threads about how folks deal with CNC+laser jobs.