What should be considered when building a natural stone wall made of slate?

So if the walls were only knee-high, I would also save myself the mortar. But at up to 1.8m high, that is too unstable for me.
: They are completely different sizes. Some small, some large, different heights.

Here are also a few pictures of my inspiration. Mortar was used there as well. It is a hotel in Sopot/Poland. In my opinion, absolutely cool work.

Looks great - and like professional work.