Rhododendrons should do very well in Allegheny County.  Rhododendrons and azaleas prefer similar growing conditions: cool, moist, well-drained, acidic soil (pH between 4.5 and 5.5), partial sunlight (morning sun and afternoon shade), and protection from strong winds. Before planting, mix organic matter into the planting site. Azaleas will generally tolerate drier conditions than rhododendrons. Avoid planting these shrubs in poorly drained compacted soils, low areas that collect water runoff, and locations near downspouts. These sites will often cause root rot issues.  This link will provide further information:   https://extension.umd.edu/resource/azaleas-and-rhododendrons-identify-and-manage-problems/

As far as other native shrubs, for your area, Extension recommends Smooth Hydrangea, Common Witchhazel, Mapleleaf Viburnum and Black Chokeberry.  Good native perennial choices include Blue Wood Aster, Butterfly Weed and Cardinal flower, but each plant should be looked up on the UMD Extension website for the best conditions.

I hope this is helpful.  Debbie