Yeah, I was a little proud of that when it turned out so nice!
(For the record: It fits a Takachi Takachi WH145-33-M3 . All of those crosses mark points of particular interest for my project - locations of the enclosure’s screw towers, mounting holes, switches, etc.)
I’ll have to look through some old backup files and see how many dimensions I have, beyond the basic circumscribed rectangle. For the corner notches I started with Takachi’s *.DXF file of the enclosure interior; then told LibreCAD to make a circle with radius 0.8mm larger than the screw towers holding the case together; then created tangential lines from the 90 edge points to the rectangular outline. Most of the arcs were generated by telling LibreCAD to convert a corner to a radius; the two diagonal lines near the center of the board were created by telling LibreCAD to find a tangential line.
Like a lot of us say, if a KiCAD outline goes beyond a basic rectangle with rounded corners (and maybe a simple notch or two), you need to use another CAD program to define the outline. We hope that in the future KiCAD will include some of those more sophisticated drawing tools.