You really don't want to just jump into buying all this expensive equipment if you really don't know the purpose of the system. Decide what you want to do first then... we can assist you considerably easier and cheaper.
The AMD firepro W7000 you mention, is all over the place for a referb card (not new) as well its 4+ years old. Even newer cards (gaming) have almost 2times the performance of this card for a around the same cost if not cheaper.Now I understand yes professional cards do have drivers that are great at doing some things, and some programs require the professional cards to activate features. Though some things you just need a standard, cheap gaming GPU to do what you need.
Really think about what you want to use it for. Most likely you can game with any card, you just might have to downgrade the graphics to run smoothly depending on if you go a professional card or a gaming card. I've been telling IT people for years at least what I do in my daily job... a gaming card not only is it cheaper (considerably) but faster then most professional graphics cards as we DO NOT use the required features for using a professional card at all.