Predator control is the first place to start. Then you have your cover....which it sounds like is pretty good. You might want some plum thickets. Sorhgum is a good choice for upland food plots and the thing to think about is upland birds love edge habitat. This constitute where habitats meet such as timber edges,field edges,fence rows,tall grasses, ect. Any time you have 3 or more of the habitats that meet at a certain area you will find more birds concentrated there because they have everything they need in one location. Also you might think about disking small rows in your food plots and tall grasses. This will allow some broad leaf plants or "weeds" to grow and creates excellent brood rearing cover. Raising and releasing birds is not a bad idea but before you do so i would make sure the habitat is best suited for them. You've got a good start though