Let's keep things simple. Mature trees and shrubs do not need additional fertilizer once established, so just mulch and water the first year. All the plants you mentioned can use the same general-purpose plant food. I recommend a slow-release plant food such as Osmocote. Follow the instructions on the label.  For potted trees and shrubs, use half a teaspoon in the spring, adjusting the amount according to the container size. Once these seedlings are transplanted into the ground, I would not fertilize them at all, assuming you have normal soil with some organic matter.  I love that you are growing volunteer seedlings of your Rose of Sharon and Redbud. Be sure to keep the soil slightly moist, but not wet, and with good drainage. It sounds like you'll have a beautiful garden soon. Keep growing, Marianne Binetti