Did you use the soil as it was in the bag, or mix it with things to make it drain well?
I agree that allowing it to fully dry is a good idea. The growth pattern of a plant grown like this one is conducive to rot if it is allowed to sit wet. When you do plant this beauty, be sure to use a well draining mix...meaning it's not going to be easy to keep it alive in soil straight from the bag. I can give you some suggestions on easy ways to mix soil if you need them.
Do not worry about the ring on your terracotta pot. All terracotta pots end up with that patina, or even algae, depending on the conditions under which they are used. White is whatever the clay leached out of the wet soil. It is a good thing.
Good luck with that gorgeous plant! I inherited one from my mother. After my father passed away the plant was thrown out into a flowerbed because it was assumed dead. It spent a winter, complete with many days below freezing. When spring came, I was organizing my mother's pots, and discovered new growth on the plant that was presumed dead months earlier. They are more resilient than you realize, but overwatering or sitting in wet soil, and rot, is a certain death.