Doing those seemingly unfitting concepts in an engine not meant for it, will be great for learning. If you are familiar with Unreal, most stuff would be just level design and one shooter/hack&slay is like the other. Sure, game design is very important and all, but you mentioned to want to learn to code. Having Dark Souls mechanics is almost meta to all this. You could have a Dark Souls mod in Skyrim. And now that I mentioned this and had a look, of course, such mods exist already.
And if you did a cookie clicker in Unreal ... wow. Maybe probably I am mistaken about the capabilities of the engine, but a 3d incremental clicker game is something I do not remember seeing.
But maybe I misunderstood, and you do want to implement core principles via level design and event scripting. You probably aim to learn both this and coding.