The spot size of the laserdiode is about 0.05 - 0.1 mm. I can easily route two or more times the same pattern without making the lines thicker or having double lines. So far my practical experience.

The stepper drive achieves with 1/8 microstepping resolution 1600 steps per Rotation. 360 degree Rotation of the steppermotor means 40 mm of belt length. So the theoretical resolution is 0.025 mm per step.