Most of the biplanes that I have built over the years have from Zero to Neg.1 degree Top wing and Positive +1 to +2 on the lower wing. The difficulty to your question is what type of flying are you going to do because Stab incidence plays a major role in determining the type of flight you are trying to achieve. Most stabs are set at a positive number -- this will allow the aircraft to fly at a slower speed but if the stab is negitive then the aircraft will fly faster and you will have to rethink your incedence for the wings but, aside from all that it is good practice to have the lower wing stall first so you will be able to have smooth control throughout the flight envelope.
Hope all the babbling helped.
Dr.Tim