Greetings, The flowering dogwood appears to be showing signs of summer stress such as mildew, limited nutrients and heat.  I suggest you get it planted as soon as possible to get acclimated before winter.  With fall planting, I always recommend applying a ring of mulch for insulation and moisture retention.  The red osier will always want to be a multi-stemmed shrub as it is in the wild.  I think you would struggle with it by trying to only keep one stem.