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There is usually no need to prune this grass except to keep it neat. If this is the case, you can cut it back in the fall to keep it neat through the winter, or in late winter before new growth comes out. I would opt for late winter. Here is more info: https://www.gardeningknowhow.com/ornamental/foliage/muhly-grass/growing-muhly-grass.htm

I see what you mean about conflicting information. Many extension sites, however, did include zone 5 in the hardiness zone for muhly grass. According the following website, "Hardiness depends on the provenance. For example, plants from a Florida population will not be as hardy as those from more northerly climes, so ask the nursery about their source." So that is something to consider.
http://utgardens.tennessee.edu/pom/muhly.htm

I would say go ahead and give muhly grass a try. However, I would take extra measures to protect it during winter. Do not cut the grass down when mulching - the foliage will help insulate the crown of the plant.

For more information on the care of muhly grass, please visit the following link:
https://www.gardeningknowhow.com/ornamental/foliage/muhly-grass/growing-muhly-grass.htm

There are many different varieties with variations in colors.
Here are a few links for you.

http://www.clemson.edu/cafls/demo/plant_profiles/muhlenbergia_capillaris_white.html
https://www.gardeningknowhow.com/ornamental/foliage/muhly-grass/growing-muhly-grass.htm

Muhly Grass can be grown in large containers.
Use a rich loamy soil and make sure the container has good drainage.
Watering is key with container plants and you need to make sure you check the soil, daily when temperatures are hot and conditions windy.
Watch for signs of the plant becoming root bound, center die out is an indicator.
Muhly Grass is hardy down to zone 6. In a container you will need to provide extra protection and even placing the container in a garage or shed would be best. The roots are vulnerable to freeze, so if they thaw and refreeze, the grasses can die off.
Most people leave the grass for winter interest and prune in the spring.
I certainly can see cutting the grass for use in dried arrangements.

https://www.gardeningknowhow.com/ornamental/foliage/muhly-grass/growing-muhly-grass.htm

In a container I would give them at least 18 to 24 inches apart.
You have to allow them space to spread out, both the grass and the roots.
Make sure the container has adequate drainage and that you do not overwater the small plants in a large container.

https://www.gardeningknowhow.com/ornamental/foliage/muhly-grass/growing-muhly-grass.htm

Prior to blooming and after flowering the ornamental grass is a lovely green graceful grass.

https://www.gardeningknowhow.com/ornamental/foliage/muhly-grass/growing-muhly-grass.htm