Be realistic about the production schedule. Even the most straightforward sites take six to eight weeks to develop; a lot longer if you're not organised! It's far better to spend a month getting the content and site architecture right first time than having to pay extra for a rework half way through the development process. And consider this: in my experience, the single most common factor that delays the launch of a site is the wait for the client (you) to deliver the content.
Plan for future expansion now, if possible. There are always new ideas and projects in business, but you'll save a lot of money on redesigns and rebuilds if your site has the extensibility built in from day one to incorporate that new line you're only just thinking about today.
Next: Putting it all together