Hi there,
Apologies for the late reply.

You have named a lovely selection of plants. For successful companion planting, it's best to match growing requirements. Here are some parameters for each. I hope that they will provide you with enough information to make a decision.

Clethra prefers moist, sometimes wet, acidic soil with organic materials and tolerates short periods of drought and flooding once established. It will tolerate full sun to partial shade but not hot dry site

Clethra alnifolia (Alderleaf Clethra, Alderleaf Pepperbush, Clethra, Coastal Sweet-pepperbush, Summersweet, Sweet Pepperbush) | North Carolina Extension Gardener Plant Toolbox (ncsu.edu)

Black Cohosh grow best in shady or partial shade with fertile, neutral soil, and regular watering. It’s a native to North America, is not invasive but is toxic to humans and pets
How to Grow and Care for Actaea (Baneberry) (thespruce.com)

Barrenwort is one of the best ground covers, staying put, and tolerate dry shade.
Barrenwort: Growing Guide to Perennial Ground Cover Epimediums (gardenista.com)

The soil under oak trees tends to be dry in the summer and moist in the winter.
What Kind Of Ground Cover Grows Under Oak Trees? A Comprehensive Guide – AlmostGrass

Hickories also has a taproot so plants with shallow roots should be relatively safe if planted nearby
What To Plant Under Hickory Trees (gardentabs.com)