Landscape fabric and 1" crushed stone under the deck is ideal...it is pretty standard around here. You can then design plantings for either side of the stairs, and also along the outside(if it gets any sun).
I'd consider a paver job for the entire side of the house. Or maybe leave the space between the AC units for small plants. The dogs may ruin any plantings you put in, since it looks like they pee there. Pavers will be a neat, permanent, pee-proof solution.