Renovate outer wall/retaining wall (plaster crumbling / wall covering)

Hmm, if I want to clad the wall with wood, I would have to leave some space so that the wood can be ventilated and dry all around. This would make the wall significantly wider. And because it tapers, it would also be a bit of a challenge to cut the boards accordingly. I think if the plasterer gives the green light and applies a new, proper plaster layer, that is probably the best solution and will look neat.

And wall capping stones - yes, they are now just made of plain concrete. Real natural stone is much more expensive, and there are several meters here that I need to cover anew. That's why I am taking the pragmatic route: neat and functional, even if I don’t win any design awards with the wall.

By the way, the landscaper also gave me the green light for planting the "Rille" - with that I can visually enhance the boring wall significantly (cushion perennials, stonecrop, houseleek & co.).

No matter which cover plates you use, you must fill the joint of the cover plates either with a sealant e.g. acrylic or with the adhesive.
Ideally, tape off about 4-5mm distance between the plates, fill the joint with acrylic, and smooth it out.

Or if you switch to a sheet metal, clamp a drip edge underneath.

At the stairs, a baseboard must be installed that, of course, is also sealed at the wall. Alternatively, the baseboard should have been installed before plastering and plaster should have been applied onto the baseboard.

Look where I pinned a "Like". I would probably contest the "Gräbele".