Wharever it takes to get 650 -700 sq inches of area.

Bearing in mind that Mike's A-26 is a profile scale model, not a stunter, I would think that something less expansive would be a better bet. I'd take a look at 55" span or 500 sq. inches, whichever is bigger. As always, lighter is better, up to a point. If it is too fragile and constantly needs repairs, then you built too light. Repairs do weigh more than building it a tad bit tougher to start with. It also depends on what your flying surface is like...cow pasture or smooth asphalt.  Steve