I'd also check the calculations on your tailplane volume coefficient - looks visually quite low to me, which could give you longitudinal stability and control problems: solveable technically with FBW, but there's really no reason to. In this application you are better of with something that has reasonable natural stability - you've no real need for combat level standards in manoeuverability.
Darrol Stinton's books "Design of the Aeroplane" and "Flying Qualities and Flight Testing of the Aeroplane" will lead you easily through the calcs.
G