The problem with FP is that MS has abandoned any development of it. A lot of hosting providers are no longer support it. Although sites built with Expression Web do not require FP extensions, if you're existing site *does* use them, you are in for a total re-write
You might want to consider going with a Content Managed System (CMS). Some examples of this are Wordpress, Drupal and Joomla. Advantages of a CMS are:
1) Content and Presentation are separated
2) Content submission and editing can be done via a browser - no software is required on your machine.
3) User Management - a CMS supports private "members only" acccess areas.
4) Add-ins; a rich universe of addins such as shopping cart, gallery, calendar/scheduling are available.
A number of people here (including myself) use a CMS in one form or another:
Luminous Landscape
Nick Rains has a gorgeous site using Joomla -
http://www.nickrains.com/John Paul Caponigro -
http://www.johnpaulcaponigro.com/Wordpress is a super easy way to get started - give it a try.....