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It is a pretty rapidly growing grass. I can't give an exact growth, as this is influenced by weather, soil and care, but I think you can reasonably expect that they will double in size in a year.

It may simply be going dormant. This article will help determine if your plant is still alive: https://www.gardeningknowhow.com/plant-problems/environmental/how-to-tell-if-a-plant-is-dead-and-how-to-recover-an-almost-dead-plant.htm

While there are guarantees, it is certainly possible to overwinter these tender perennials indoors. Be sure to cut it back first, to about 3-4 inches and water well. Then refrain from watering except once a month to prevent the plant from becoming too dry. Once warmer temps return in spring, return it outdoors and give it a boost of fertilizer to stimulate new growth. Hopefully, it will respond favorably.

This article will help you: https://www.gardeningknowhow.com/ornamental/foliage/fountain-grass/fountain-grass-pruning.htm

Hedge trimmers will work to trim back the fountain grass.

It will not survive the winter in your area. You can try digging some up and storing it in a basement or attached garage. That should keep it warm enough to survive the winter and it can be replanted in the spring. Just make sure to give it some water once a month or so. It does not need light and will be dormant and dead looking, but will just be "asleep" while you store it.

It can survive in temperatures down to 20F. If it does not get colder than that where you are, you should be fine.