The nice thing about having someone unqiue to each area is they should "theoretically" be an expert in that area. Most of the time that really isnt the case and I suggest you search for some that is disciplined for the most part in all.

I would wholey reccommend skipping the Photoshop stage. Find someone who can design/mockup wholey with html and css. This will reduce overhead of having multiple people while speeding up your pipeline.

Hope this helps out a little!