Hi Sarah
You might want to start small - with 5 to 10 core pages (or whatever is "small" or "core" for
your site) and then set a goal to add x number of pages to the site each week or each month.
If it is a large site, this works very well. If it is a small site, step one is getting it up - then you can focus on the marketing plan.
Whichever direction you decide to go, I highly recommend that you optimize your web pages for the search engines
as you go. If you havent already done keyword research,
that is where you should begin. (You can use the at WordTracker) This will help you to understand your target market better and get an idea exactly what they are looking for... so that you can go back to your site plans and make sure that you are delivering just that