Alright, then I misunderstood the "they." I can/we can do the cleaning. That's not the problem... We'll see, maybe I'll plaster the wall and if it really should fall off sometime, a covering will go on it.
It is also professionally done by a bricklayer here
Actually quite simple. Prime, apply reinforcing plaster with mesh, and then your desired plaster on top (probably similar to the one on the house)
Just make sure that he also embeds mesh and that he doesn't use some cheap reinforcing plaster, there are big differences and that stuff is expensive. People often try to save on that.
They will probably now use formwork blocks at the retaining wall on the property boundary, which will be clad with [Rhombusleisten]. We will probably support the terrace with L-blocks.
But today we first buy a mini excavator so that we can even start at all.