I would contact your county extention or the Master Gardeners in your area for ideas. Zone 3 gets pretty cold in the winter. I am in Zone 5 and sometimes we get below 0 for several days, but not like you.
I would be sure to cover your plants with good mulch in the winter to protect them.
Also, I would wait a few year before dividing your hostas. I love mine when they are huge. They cover more space. I have had mine in the ground for couple of years.
Some of my ferns have a diameter of 4 feet across. It has taken years, but . . . fill in with impatiens and mulch iwth small bark to give a finished look.
You might want to place some larger decorative rocks and plant around them.