Most excellent. So what would be the recommended set of plants (and which order to plant them) to rescue typical sandy central Florida soil with its thin layer of grass?

After seeing One Straw Revolution I'm trying to imagine what the Central Florida parallel for this would be. How can we do more by doing less?

I read One Straw Revolution and found it quite interesting. Some of his soil improvement ideas are revolutionary, for sure.

Here I think the key would be trees and shrubs. The only thing that ever looks really good here is the woods. Your biochar experiments are likely a good start. Tithonia diversifolia is a good bet, too, as are perhaps giant grasses like Sudan grass.