If you don't use sheathing, I don't think you'll get an engineer to sign off on your plans, I'd bet. Why not just make your floor 4" wider than your frame and put a full 2x4 wall outside the frame, instead of infilling? It would permit you to slide your drywall behind the posts, and make your stud layout much clearer and easier for everything from sheathing, to siding, to insulation, to drywall.