Biplane incidence can vay depending on your application.

First, you will probably need a little positive incidence in the stab. This is due to the wing wash from the top wing.

Next, think of the wing with the most positive incidence as stalling first. Say, for example, the top wing has positive incidence and the lower wing is at zero. With this case, the top wing stalls first. To visualize what happens, imagine you have removed the top wing. It is stalled. Now we have a plane with the lower wing only. This new "plane" has the wing set pretty far back and has a long nose, so it is more than likely nose heavy. This means it will recover from the stall fairly quickly. Nose heavy planes also aren't snappy.

Now look at a plane with the lower wing at a more positive incidence. The lower wing now stalls first. Imagine a plane with the lower wing removed. The top wing is forward so we have a tail heavy plane that tends to be fairly snappy.

These scenarios are for normal stagger and a reverse stagger would have the opposite effect.

A lot of this in mitigated because most RC biplanes use only a small amount of stagger as opposed to full scale planes where a full span stagger was common.

So you can see you set your bipe up depending on how you want it to fly. Do you want a snappy acro, fun fly type bipe or a more sedate one. I tend to like the more snappy ones, but for a scale Stearman, you might want a more sedate flying plame.