What's your question? Ask

You can cut the dead flowering stalk almost all the way out. Leave the growth until it is time for dormancy. This article will help: https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/growing-calla-lilies-and-care-of-calla-lilies.htm

How much of a gambler are you? Success in keeping calla coming back in your zone will depend on how wet your soil is, how severe the winter is and whether you have snow insulating the soil from repeated freeze and thaw cycles. There is wide variability in winter hardiness so a general answer to your question is not possible.

Yes, cut the dead foliage and stem down. The tuber should have survived and be sending up new growth once the soil warms. If it has been a while, this is a good time to divide your calla lily. https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/dividing-calla-lilies.htm

Soil should be moist, not wet. Wet soil will cause root rot in calla lily. Here is an article that I hope you find helpful. https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/yellow-calla-lily-leaves.htm

This can, actually, be for several reasons. A photo will help me to make a better judgment call.

This can be due to over, or underwatering or due to a lack of light. Worst case scenario will be a fungal infection, but I'm hoping to rule this possibility out. If you can provide a photo I will be more than glad to help.

This article will give you more information on the care of these in the meantime: https://www.gardeningknowhow.com/ornamental/bulbs/calla-lily/drooping-calla-lilies.htm

Calla needs moist soil to thrive and even though you keep it watered, the plant roots may not be able to replenish water as fast as it is losing it. This is especially true if the plant has outgrown its pot or if it has been in the same potting mix for several years. Soilless potting mixes break down leaving little material to hold water. Calla will grow in very wet soil; try putting your pots into trays that contains water. When you are due to repot, mix compost into the potting soil. Do not use a mix that has bark chips. You don't want a fast-draining soil with calla