Answer: Unfortunately, based on your description, I am unable to make specific recommendations with any confidence as to plants that will do well in that location. I would strongly suggest you work with your local professional nursery staff, possibly also your local county extension staff, and even possibly consider hiring a garden designer with a good background in horticulture to help you. These professionals should be able, based on on-site information, make far more accurate recommendations that I ever could long distance.
That said, I would surmise that the location is both shady and also relatively dry. Astilbes and ligularias in paritcular, and many other shade plants as well, simply will not tolerate dry conditions. For this reason, you may need to reconsider some of your plans and mental images of what you want for that area.
It sounds like this is a tough site and you really want to achieve some significant results here. It's great that you are researching the options prior to planting. Since it is such a prominent part of your landscape, I really would suggest obtaining some serious professional design assistance. If you do not want to pay for a detailed plot plan, a designer might be willing to do an onsite consultation for an hourly fee.
I'm really sorry I can't be more helpful. Best of luck with your landscaping.
Q&A Library Searching Tips