Go ahead and plant. Most perennials will be hardy in your zone despite a freeze. That is what makes them perennial, as they can survive winter and come back year after year. They will appreciate a good mulch on top of the soil as newly planted perennials can be heaved up out of the soil when there is a hard freeze. You may experience some die back this winter as the plants were not well established but just cut back any brown or dead looking growth in the spring and new shoots should appear from the roots. Sounds like you will have a perennially beautiful  garden. Keep growing, Marianne Binetti