48806 event and client management db

I've attached a detailed brief of this project. The current site is [login to view URL] and we want to make it completely database driven with user and admin sections that will enable us to run and manage events from anywhere in the world. The organisation is run by volunteers over the world so a simple but effective site is required. I guess there are two levels to my overall aims - firstly the programming of our requirements, then the design of new pages for the site. I am not sure if this is the recommended way to approach a facelift of a current website so suggestions on the best course of action welcomed. Thank-you.