That looks like a wonderful place to work with. If you could, to save your backs, I would get a crew in there to clean out all the dead and weeds. It sounds that you have a good idea of where to start. Definitely hosta and fern, goats beard in the back. Chocolate Joe Pie Weed is a great contrasting color and has late fall white tiny flowers that form little balls that almost looks like foam. Heuchera have so many leaf colors and are not invasive. Helleborus are so beautiful in the early spring and the leaves are beautiful all year.
There is a shade gardening forum that I would go to for questions and suggestions.
Happy Gardening. I want to see the finished project.
One other thing. Mulch is a great weed deterrent and you need less water.
