Your FIRST step:
Is flawed... since that's a backwards approach to "design". Photoshop is NOT a design tool no matter how many tools claim it is, or use it as such out of ignorance of ACTUAL design and how it relates to things like a dynamic UI (or as it's called in HTML/CSS, responsive elastic semi-fluid layout), accessibility norms, and limitations of the medium.
So the first thing I'd suggest is axing that from your plan. If Photoshop were to be used at all it should be for a last-minute paint-over, something we really DON'T need in most cases -- PARTICULARLY on applications -- as CSS becomes more and more capable.
Content dictates markup, content + markup + media limitations dictates layout. NOT the other way around.
Art is only a small part of ACTUAL design, so starting out with art is utterly and completely back-assward.