spinneyboi10
It looks like the scoring equation does not have a time factor.
You have mentioned a take off within 100 ft but presumably to qualify the 'flight' has to met some criteria.
With no time limit there is advantage in flying slowly as fundamentally the power to fly is proportional to speed.
You do have a wing span factor but not on wing area or, as has been pointed out, on the number of wings.
This suggest a broad low aspect ratio (4:1?) wing or wings. Low aspect broad chord wings have 'depth' so are much easier to build strong, light and rigid.
You are building a 'payload' plane where structural weight is a key factor to maximise payload for a given amount of power (1000W).
As you are carrying at least one football, which suggest the fuselage has to have some depth, a biplane could make some sense.
If you are only going to carry one ball it could go in the nose ahead of the wing(s) with its weight countered by the much smaller but heavier steel plates behind.
Large wing area slow flight has the advantage of a low take off speed so avoiding the need for additional lift devices. Keep it simple and light.
Set yourself a power to weight target, say 80 W/lb (you could likely get away with quite a bit less), to get the 'target' all up weight = 12.5 lbs. Consider a 'slow flying' wing loading of 8 oz/sq ft. You would need a wing area of 25 sq ft. If it was a biplane each wing would need 12.5 sq ft. Say a span of 8 ft with a 1.5 ft (18") chord (aspect ratio 5:1). Even with a 'simple' wing section the wing is going to be over 2" thick.
With these sort of dimensions it should be possible to carry a 6.5 lbs payload in a plane that only weighs 6 lbs. It will fly at 8 to 10 mph and have power to spare. With such a target achieving the strength to weight of the air frame is likely to be bigger problem than the efficiency of its aerodynamics.
Just my ramblings at the problem but it is the sort of process I went through to build a plane that had to carry 50% of its weight as a payload but to do so using the lowest possible power.