I don't think you need a mediator until you have reached the point where the two of you can't agree.
I have never been divorced but I just watched my BF go through a very expensive one. In hind sight, the one thing I would tell him to do from the start is write out a list of what you want, in all the areas where this is important. So, for example, if it were me, I would start with:
I WANT:
everything I came into the marriage with (the house, my car, all the living room and dining room furniture, etc)
YOU CAN HAVE:
everything you came into the marriage with
I keep my 401k and you keep yours.
I keep what my parents and family and friends gave us and you keep what yours did. Except, can I have the clock?
Whatever, but you get the idea, right? Start focusing on what YOU WANT.