Seeking practice similar to my background (engineering), I ended up finding 50 CAD Exercises and decided to drill through them and practice moving around in the Blender viewport and manipulating geometry. It absolutely does not follow hard-surface modeling techniques in Blender (largely because I do not know them yet) but I hope to revisit in the future once I’ve learned. I think it might also be good practice for Boxcutter once I start learning it.
Couple this kind of design with a 3D printer and the possibilities are limitless! :)