This is the house. I would like to put window boxes to the bottom two windows. Thanks!

There are other options for freestanding window boxes if you find you cannot attach them to the house.

Dryvit is just an EIFS - a rigid insulation board with a synthetic stucco on top of that. You simply fasten through the insulation board to a wood support, like a stud or the (framing) sill below the window.