The default setting is for the origin in the CAD (0,0) to correspond with the workpiece origin (home position). When the job has completed your machine should return to 0,0 so you can change the material and start again.

If you are using my firmware and parameters, 255 is maximum power but if you use other software or firmware the Grbl parameters may be changed in which case 1000 may represent laser max. You would usually adjust feed rate to burn more or less but you can also change power, it is more optimized to keep power at max.