Rotary, that's an interesting take on the topic. Up to now I had only read about gapping the wings based on chord.

Hobden, you asked about stagger and CG.

Stagger is not a requirement for a biplane and has minimal effect, if any, on the flying of the airplane. If you look through the history of biplanes you'll find that they stagger, both positive and negative, was added pretty much only for pilot visibility reasons or to achieve a good CG with minimal issues. Non staggered biplanes, like some of the racers of the 30's and the Dehavilland Gypsy Moth, flew just fine with no stagger or upper wing sweep. Here again the upper wing sweep is related to allowing the pilot easy entry and exit while shifting the wing area back at the tips to best achieve the CG rather than for any aerobatic reason. So the stagger, within reason, is up to you and your esthetics. Within reason means that the wings should overlap by at least 1/2 a chord or you may, or may not, find that it starts to have some odd effects.

The slickest CG determination I've seen is a trick that Tall Paul offered a while back in one of the RCU forums. This was that you "look" down on the top view of the plan and use the wing area that you can see as the equivalent "single wing" and use that view to determine the MAC and pick your CG at 28 to 30%'ish of that fake MAC. So a typical staggered setup would use the leading edge and tips of the top wing and the visible portion of the tips and the trailing edge of the lower wing as this CG determination wing. So a non staggered wing would just use the single wing to find the MAC.

And a last hint for bipes. Due to the interference effect of the wing gap biplane wing areas are often "derated" compared to monoplanes. If your gap is one or more chords you can take your effective wing area as being probably 90% of the true total area. For a gap of about 0.8C the wing should be derated to probably 80%. And for a gap of 0.7C the derating would be around 65 to 70%. I've got nothing scientific to base this derating on. It's just that it was mentioned in a few design articles by prominent model biplane designers over the 40 years of my magazine reading. But it's most likely related to that material in Phil's post where the maximum lift coefficient is lowered by the gap so the wing tends to stall at a lower angle of attack as the gap is made smaller. So to achieve the same stall speed with a bipe requires more area to lower the wing loading.

Or use my trick and just make the model come out lighter.