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Fertilize monthly with an all-purpose fertilizer beginning in spring and continue throughout the growing season.

It sounds like it may have a bit of transplant shock. The purple fading is the flower itself dying, which is common for plants in shock. They tend to jettison the flowers first in an effort to conserve energy. The leaves are then affected next.

Increase water and give it a a little bit of sugar. Mostly it just needs time and may lose its flowers regardless of what you do. This article may also help:
https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm

You may also be interested in this article on how to get callas to rebloom:
https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/make-calla-lily-bloom.htm

Do you mean just eating the blooms off the top of the plant? If so deers and rabbits will eat the bud. Buy a deer and Rabbit spray. Home depot has it. Stay the plants after each rain.

The plant is likely suffering from shock as it adjusts to the new environment and this normally clears up on its own provided you keep it well watered. Here is more information that will help: https://www.gardeningknowhow.com/plant-problems/environmental/learn-how-to-avoid-and-repair-transplant-shock-in-plants.htm

This article will help with growing your calla lily: https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/growing-calla-lilies-and-care-of-calla-lilies.htm

Just prepare the planting hole around the same depth as the pot it is currently in and water it well. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/growing-calla-lilies-and-care-of-calla-lilies.htm

No, you don't have to deadhead these plants but it will not hurt them to do so.