I would forgo the black walnut trees as this species is highly-cited as an unacceptable yard tree (I receive numerous complaints every year regarding black walnut fruit, staining caused by walnut husks, etc.).
Furthermore, interplanting black walnut and apple trees is not advisable due to black walnut's alleopathic effects on certain plant species, and unfortunately, apple is generally considered to be susceptible to juglone.
To read more about black walnut alleopathy and plant susceptibility to juglone, please visit the following university Websites:
Your fruit tree spacing may be a little tight, depending upon species selection: semi-dwarfs generally need about 15 ft of spacing between trees, whereas dwarfs only need 10-12 feet spacing between trees.
For more information regarding fruit tree selection, please submit your questions to the Hort Corner forum: