Finally talked to the building inspector about the slab. He indeed had some questions about it, but it all went well, and he even complimented me on the framing, particularly the design. I have the go-ahead to continue.
A compliment from the building inspector is damn cool, yo.
So I'm full-on to start the installation of the insulation. I seem to have a lot of pink Styrofoam Dow Corning™ extruded polystyrene foam around, perhaps I will use that.