Is 3-4' the length? What is the width? What direction do they face?

Yard faces west. Gets a ton of direct sun for most of day. I haven’t purchased planters yet but was looking at the corten steel planters 14 w x 14 d x 48 “ length. But I’m completely flexible if a different size is more appropriate based on what I’m planting. Thanks

Cold hardy clumping bamboo makes a great evergreen privacy screen. And will grow faster and produce the needed privacy faster than any other sort of planting. Look at any of the Fargesia species for this.

If you want variety, I'd go with smaller containers of other plants that you can decorate your deck with, incorporating whatever color, texture and sizes that suit your fancy.