You can grow tons of stuff in that light. Certainly Himalayan box (sarcacocca) I don't know about regular boxwood. Yes to climbing hydrangea. Any hydrangea should do fine.
Keeping in mind that I'm on the edge of zone 7/zone 8 and am growing stuff that might not be able to take your cold, here's what I have on the long, long northeast side of my house:
Sasanqua camellia
Lace-cap hydrangea
Daphne odora
Gardenia (might not be possible in your zone)
Southern shield fern (for the darkest corners)
Royal standard hosta
Helleborus orientalis
Nandina domestica
Hammamelis mollis (witch hazel)
Vinca minor for ground cover
Confederate jasmine (probably not possible in your zone)

You can grow boxwoods in the shade. I planted some as foundation plantings last summer in the deep dark AND dry shade on the north side of my house under a 5 ft overhang, not only does it not get any sun, it doesnt get much in the way of water either. they are doing GREAT! The holly compactas I planted with them.. not so much! (aka they are dead!)