Its great to have consumed that Beth Chatto book (literally of course
)
I love all the Heuchera plants - very attractive indeed. There are some plants in your list that Ive never grown (Waldsteinia, Houttuynia , Bletilla ) so -isnt that what makes this forum interesting! Get some photos!!
Ophiopogon is a very good choice.
Theres one Campanula I'm really fond of, but dont know if it would survive it those conditions
Campanula carpatica - available in Blue and in white. Nice and neat, about 12ins high.
I grew mine from seed (I dont think you'll have time for THAT
)
Another plant suggestion:
Actaea simplex (Atropurpurea Group) 'James Compton'
I have this plant, and it is a beauty. I bought it for foliage. It has never flowered. Ive moved it a couple of weeks ago to a damper position in the garden.
It really does need moisture. It shrivels up if allowed to go dry, hence the reason for the move.