Are dialogue and character literary elements or literary techniques?
I'm trying to create a list of elements (things found in most stories) versus a list of techniques (things the author uses to enhance the story).
As you suggest here, "literary elements", as a term, is more broad than "literary techniques", and so can be said to include many items that would also fall into the category of techniques.
Both dialogue and character then would qualify as literary elements. According to your project here, each would fit this category because each is found very commonly in most stories.
However, we can also say that dialogue is a specific literary technique. Dialogue does not appear in every story and is often used to create a specific effect, often to help create character and atmosphere. For this reason, dialogue best belongs to the literary techniques category.
Character is a fundamental aspect of every narrative. There is no such thing as a story without a character, even if that character is only a brooding, detached narrative voice. Many literary techniques are used in the service of creating, defining and deepening character. For these reasons, character best fits into the literary elements category.