On: Making my first robot as a software engineer

[remram]

Wouldn't you need the Arduino to do the inverse-kinematic calculations if you want to interpret gcode?

[dekhn → remram]

See fluidnc http://wiki.fluidnc.com/en/config/kinematics as an example where you can get kinematics going without too much effort. It also has links to more pen plotter implementations to learn from.