zepher to the daylily addiction! You have reached a point of no return! Before you know it, your number will be in the 100's and will frantically look for space to expand your daylily beds.
I am relatively new at this but zone 4 is pretty cold. Since you are buying from Maryotts and they are located in CA, the plants you get may not be accustomed to the cold yet. If I were you, I would plant them in pots and keep them sheltered from freezing. I am in zone 6 but just to be safe, I will be mulching the newly planted daylilies heavily in December.