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This plant is hardy in zones 7-10.

You should be able to winter over indoors. It will die back in the late fall or early winter.

That sounds like powdery mildew. You can remedy this with neem oil, rosemary oil, garlic oil, and/or lavender oil. Here is an article for more information: https://www.gardeningknowhow.com/plant-problems/disease/powdery-mildew-homemade-and-organic-remedies.htm

Acanthus literally means thorns and there is speculation that it is responsible for the Crown of Thorns in Christendom. It could be you are accustomed to cultivars that don't have thorns but I think you are spot on with your genus guess. It is invasive in some areas and spreads by underground rhizomes.

What I would do would be to plant an empty pot in the ground, and put the plant in a restricted container inside of this pot, so that it can be removed. This will take diligent trimming of the top and the roots each year, so this design will help it to be much easier for you. It will combine the aspects of container, and in ground gardening, so that you can control size, while still maintaining a professional appearance.

Ants are naturally attracted to the flowers on your vine.
This link will help you.

https://www.gardeningknowhow.com/plant-problems/pests/insects/keeping-ants-off-flowers.htm

It will recover on its own, likely. Chelating the soil would cause more damage to the plant than it would fix at this point, and is best done while nothing is planted in the soil.

This article will help you to know what care they require:

https://www.gardeningknowhow.com/ornamental/foliage/bears-breeches/grow-bears-breeches-plant.htm