Nice layout. I only have a few comments to make, I am as well expirementing with proper plant placement.
The two foreground plants you have are quite slow growers. It may take awhile to get a nice carpet. Also, with the amount of Stargrass you have, you might have to spend quite a while pruning them! I hear they grow like a weed. If the "Carolina Fanwort" is a Cabomba, it may actually get bigger(or same size) than the Stargrass behind it. The height should not be too much of a problem in 30g, it just might block your view of the scenery behind it.