I don't think any biplanes have used dihedral wings... might be wrong though.
Indeed, You are wrong. Lots of biplanes have used dihedral wings including such types like BE.2, DH.9 or Bristol Fighter. Lots didn't, lots only on lower wing.
My comment about the wings is that they are too "flat", that is, they lack any attempt to show their airfoil, while the struts between them should be "more vertical" (looking not like
N, but I I , as
N would make sense if the upper wing was much more to the forward then the lower).
APDAF
I'd say that weakest part of this design is the undercarriage - typical (for the era) one with the tail wheel would be better, I guess, and for safety You could add a front wheel a la Caproni Ca.3.
http://en.wikipedia.org/wiki/Caproni_Ca.3
Also, IMHO the engines are bit too far to the rear, even for a pusher.