YJ,
I don't know what your 1/2A Skylark looks like. That would help. It would also help to understand your performance expectations for the plane. Scale(ish)? Loops? Wingovers? Fly only in the dead calm, or in light breezes? Or full stunter?
I can say that a Baby Bee only has a given amount of power. Since these engines are often not stock and came in different vintages you will want to know if it is a single bypass or dual bypass engine. There's a noticeable power difference. And, has it been swapped around for other performance parts? High compression head? Larger venturi?
In full-scale aircraft design, the engineers use power loading as a metric. Same ideas apply here.
Upsizing the span by 150% makes it 34.5 inches. If you only want to fly level, upright, and in calm wind this gives you your floaty glider. I have a design I call the Spring Break Special with 32" span and uses a Cox Medallion. With the Bee, I would keep it (well) under 30" unless you are after the floaty thing.
You are increasing the drag with the larger wing and you need to have enough power to get it up to the speed you want to fly. You can offset the power requirement somewhat by using shorter lines. There is more drag from the lines than the plane itself if the plane is reasonably streamlined. So with limited power, you can shorten the lines to reduce drag. And by all means, use either some light Spectra or .008" stranded steel to keep the drag down. The steel lines require careful handling to avoid damage.
Another way to bound your sizing question is to look at the weight. For a Cox engine, I wouldn't want the plane to weigh more than maybe 12 oz. So you can't simply keep growing the size without the weight going up or making a (more) fragile plane. The weight plays back into the power issue: the wing has to lift it, and the increased weight causes increased induced drag. If you are using a fat symmetrical airfoil then you already have a good amount of form drag from the wing.
As an example, a Baby Clown with a wingspan of 25-1/4" and chord of 5-9/16" (140 square inches) flies really nice with a dual-port reed engine. I haven't tried a single port engine, but it would likely do pretty well.
At the other extreme, consider the Baby Pathfinder. An excellent plane, by all accounts. A 35" wingspan and 236 sq. inches of area. But you are going to need a strong Medallion, a Tee Dee, or one of the .061 "half-A" engines. For a Baby Bee on a stunt capable plane you should be looking for something smaller.
I hope this helps you plan out your project a bit,
Dave