Advice requested for painting diorama base (vignette)

Mark,

After constructing what needs to be put together, I would shoot a med to dark grey primer color. The darker grey primer will help in producing the shadows and dark spots in your diorama. Your groundwork requires airbrushing  or hand brushing earth tones, then touching up several areas in different earth colors, followed by dark brown and black washes. Dry brushing  a slighter light color to highlite the rubble. I would paint the brick mortar first by painting it a concrete color. The bricks will come next by painting each brick by alternating the brick colors by darkening and lightening  the paint  so all bricks don't have the same tone. Several dark washes would follow in order to bring out shadows and details in the brick. I would also use some pastel powders for additional detailing like dust, grime and dirt, grimy walls etc. A flat clear coat seals and protects everything. Hope this points you on the right direction. Sounds like a fun project.