The Edgeworthia which I planted last autumn is showing new growth at the soil line. Should I prune this or leave it alone? Thank you!
If you want it to maintain its tree like shape, then you will want to prune these off. Otherwise, they will bush out, as they would in nature.
This article will give you more information on the care of these: https://www.gardeningknowhow.com/ornamental/shrubs/paperbush/paperbush-plant-care.htm
Best time to plant a "paperbush" bush plant from seed,
You will want to do this after all threat of frost has passed. It is best to start these indoors under bright lighting to give it a better chance of survival.
Since you are on the edge of this shrub's hardiness zone, it may need extra protection in the winter.
Here is an article that will help: https://www.gardeningknowhow.com/ornamental/shrubs/paperbush/paperbush-plant-care.htm