What to plant on and in this wall?

I’m thinking trailing rosemary (Blue Rain) in planters along the top and sedums in the cracks? I could chip off some more render and mortar to make more cracks. Any better ideas? Would the rosemary look best on its own or as a mixture with other drought tolerant trailers? We’re in SW England and this wall faces SE, so will get hot and dry. Ideally the planters will eventually be hidden.