I have only purchased one kit ( pattern & fabic for the top) and it is waiting for my attention almost a year later. I will pick out the backing after the quilt top is done. However, I have friends who have experienced NIGHTMARES in purchasing kits that don't have enough fabric and discovered too late to find same.
I usually wait until my tops are finished; by the time I am ready for backing, they have spoken to me as to what is best for back.
Evidently kits sell well because I see so many of them at quilt shows. I would suggest variety in your fabrics such as one kit with light fabrics and another with the earthy tones.
Good luck in your effort.