I want to make an island bed along the side of our backyard. Right now we have an Autumn Purple Ash that we planted 7 yrs ago - before EAB reports. That would be at one end of the bed. For the other end I ordered a Golden Glory Dogwood. I have 20 ft from the ash to where the bed would end. Should I put the dogwood all the way at the end or leave a few ft for something else or just mulch? I want to put smaller shrubs and maybe perennials in here too but no idea on where to start or what would look good. The area should still get quite a bit of sun. The small shadow from the ash goes east and west and the bed runs N & S. Some shrubs I like are:
Hydrangeas (smooth, oak leaf or paniniculata)
Weigela
Spirea
Barberry
Clethra
Buddleia - more like a perennial here
Ninebark
Open to others

Perennials - open to suggestions on ones to add once shrubs are selected or if I should skip these and just keep it very simple with shrubs.

I don't have a width or shape yet. Overall length will be 20 plus whatever we add to the other side of the ash.

Thanks.