Hi Peter,
I think the best and easiest way is to use a CAD/CAM software to draw your part (or import the .dxf / drawing file) then it can create the Gcode for you automatically applying the tool radius and offsets, etc. Actually writing the Gcode by hand seems a bit outdated nowadays.
One of the most popular range of CAD/CAM programs is made by Vectric;
https://www.vectric.com/ (for what it does it is worth every penny).
There are also many FREE softwares, one I use a lot is F-Engrave;
https://www.scorchworks.com/Fengrave/fengrave.htmlPerhaps Google free CAD/CAM software.
Tweakie.