Your contact person needs to have the authority to give approvals. Define how much input will come from people ostensibly outside the immediate project team. It is up to the designated liaison to handle them. Once the designated liaison has signed off, that should be it. If changes are wanted, the scope and price will need to be adjusted accordingly as stated earlier.
Some discipline needs to be exerted on the compulsive changers within an organization.
Finally, organize to maintain the site. Figure out how often the site will need to be maintained and who will do it, a staff member or a contractor. Budget for this and train those who need it. Get your Web team to write maintenance procedures before they leave the project and to organize site files neatly on a hard drive. Once you've researched your needs and hired a site-building team, you'll have a structure that will allow your site to come together.