Just a heads up regarding walnuts and apple trees, do NOT plant the two together.
While there are fruit trees that perform well near walnut, black walnut and butternut, apples are not one of them.
If you are interested in nut trees, try pecan or hazelnut instead.
If you are considering a walnut tree, try companion planting with plum, black cherry, paw paws, black raspberries, goumi berry, autumn olive and mulberry.