Some options:

Multipurpose native ground covers:

Cornus canadensis. White Flowers in spring, Red berries in summer, Red leaves in fall. Attract birds. Miniature forest for children. 'Fairy tales' themed. Just a mat of stems or scorched leaves in winter. Low. Stands Shadow.

Tiarella cordifolia. Soft green leaves with a foam of White flowers. Shadow. Delicated. 'Feminine'. Spring. Spreading by rizomes, but not much invasive. Visited by insects and bees.

Asarum canadense. Good heart-shaped leaves. I don't know how it stands summer, but probably well. Reddish flowers rare but hidden. Interesting at short distance, but often missed. Poison.

Bearberry. Arctostaphylos uva ursi. Low mat of 7 inches high or so. Hard aspect. Ordinated. Solid. Leathery small leaves, pink-shell bells, Red fruit and good fall color, purple dark. Needs acid soil. Slowly growing to up to 15 feet diameter, but can be pruned to keep it in shape.

Antennaria plantaginifolia. I don't know about if is too vigorous or not. White small flowers. Separated sexes. 'Dusty'. Useful for drier places, but not outstanding.

Fillers:

Native violets (Viola). Visually soft and fragile with nice blue flowers in spring. Reseed itselves on gravel and crevices, but never a nuissance.

Mitchella repens share some points with Cornus (white flowers, red berries), but is a native short creeper with small 'hard' leaves. More fragile and fragant. 'Feminine'.

Aquilegia, bulbs, ferns etc...

Grasses and taller shrubs for accent and out of season interest:

Yes, you need some grasses, they are wonderful and your winter is too long. Some candidates.

A clump of Switchgrass Panicum virgatum 'North-Wind' 3-6x3 feet. The winter spectacle in orange-rust tones deserves well the nuissance of a single cut to the soil level each year at february. Linear, vertical, upright standing even strong winds. Opaque, but could fit your needs if you want privacity in summer and a wild touch. Panicum virgatum 'heavy metal' is a slightly smaller version that provides a good canary yellow in fall (instead orange), and a strange tone of blue-green leaves in summer. Both get dormant and wake up very late when soil warms, so there is nothing to see between its annual cut at the end of the winter and June or so.

If you want a more delicate option, you could use some Molinia caerulea "transparent" (non-native) or the native Wavy Hairgrass, Deschampsia flexuosa. 12-30 inches hight, Effect transparent and delicate. Both catching light wonderfully in a non obtrusive way. Not so much to see in winter in this case, but good in summer and fall.

Black Chokeberry. Aronia melanoarpa. A very hard plant when established standing some pollution and unfavourable conditions. Middle height, 3-5 foot or so. Could be pruned eventually if needed. A little dark green in summer, but a wonderful scarlet fall color and shiny black berries that attract birds and are sour but edible. Whitish flowers with pink anthers. Aronia arbutifolia is taller and provides a luminous orange fall colour for a few weeks and many scarlet berries over green foliage in summer and fall.

Cornus sericea. Excelent dark red lasting for all winter, very nice mixed with snow. Makes a dense mat. Worth it even if you'll need to prune it once each year to keep it dense and at 5 foot or so. If you prefer greenish-yellow stems look for C. sericea flaviramea instead.

To avoid:

Aegopodium. Easy. But a monster spreading over large areas and growing fast from rizomes and discarded cuttings. Aggresive invader in NE USA.

Vinca, nice flowers, but too aggressive also and non native. You will need to keep it on place, and is not an easy task; they run around like rabbits.

Hedera. Will cross the path and you will need to prune it.