Especially with the A-4, CF is not necessary. It's a thick wing, with inherent strength advantages. A little CF in the right places can make sense on any model, but most folks use it for the WOW factor - because it's trendy and is strong enough to make up for poor structural design. If it's a concern, covering of light CF cloth between the wheel wells would be more than you'd need.

Of more importance is to make sure the controls are very stiff. Flex and freeplay that would be fine on DF will come apart at higher speeds.

I'm not a big fan of using sorghum for wing skins, as I had whole wing fall apart in storage after it was skinned with the stuff. THat's in the Florida heat and humidity though. I'd just use West System epoxy.