Digging a forest garden

In between the Palm Sunday activities, the weather is wonderful and my springtime gardening plans crystalize. I will plant heirloom (non-red) tomatoes, so my homemade pasta sauce will be bright and tasty! My Bell and New Mexican peppers grew well last year, and my experimental tepary bean crop was fantastically good. My hope is to extend organic annuals such as these to include perennial food crops in an edible forest ecology.  
The concept that I am aiming for is that of edible forest gardens, with overstories, understories, shrubs, herbs, groundcovers, all mutually supporting. A familiar example on a small scale are the Native American "Three Sisters" - corn to provide scaffolding, beans to enrich the soil, and squash to shade the roots and crowd out weeds.  A fourth sister Cleome serrulata  "Rocky Mountain bee-plant" attracts bees to pollenate all the blossoms and itself provide edible leaves, flowers, seeds, and roots.

Besides these traditional crops, I will try native Opuntia ellisiana "spineless prickly pear", 
Cnidoscolus chayamansa "tree spinach" or "chaya",  and Moringa oleifera "moringa" or "drumstick tree".  
I plan to expand the raised bed area with minimal disturbance to the existing plantings and the soil.  Extending two adjacent square plots along their common sides and excavating the space between them would create  a  4' x 12' raised bed with an existing Nandina ("Heavenly Bamboo") in the middle sharing space with the catnip, mints and other herbs.  Further excavating a second row would create a  4' x 8' raised bed with a 2' wide path between the two rows for access. 
A stronger digging shovel, a pinch point bar, soil tester and a wheelbarrow and we have begun!