If the wall is not holding back an earth load, it's not a retaining wall. It's a freestanding wall. You'll need a concrete footing, 8" depth (thickness,) whose base is below the frost line and whose width is double the combined width of all masonry that sits on it (block + stone.) You'll need rebar, embedded in the footing that continues to the top of the wall, every other block. The cells through which the rebar pass will be filled with concrete. Use truss or ladder mesh at every other course. While most of the illustrations and videos about building a cmu wall are for building structures, the principles are the same, so adapt for your needs.