One other thought here — if you do get the basic shape drawn up in Carbide Create, the way to do regular offsets from a path is to lie to Carbide Create about the diameter of an endmill, so work up the design for a 1/4" endmill, then, when you want the 1/4" rabbet, just cut on the inside and tell it you’re using a 1/2" endmill.
That said, it’s as noted, easy enough to draw:
